Custom editor layout broken in 14

Implementing a custom editor layout as described at https://documentation.bloomreach.com/14/library/concepts/document-types/custom-editor-layout.html has broken in 14.

Using the layout for a new doc type or compound type result in a long Wicket stack trace saying:

[DefaultExceptionMapper.mapUnexpectedExceptions:170] Unexpected error occurred
INFO 30.03.2020 13:04:20 ERROR http-nio-8080-exec-6 [DefaultExceptionMapper.mapUnexpectedExceptions:170] Unexpected error occurred
INFO org.apache.wicket.behavior.InvalidBehaviorIdException: Cannot find behavior with id '1' on component 'org.apache.wicket.markup.html.panel.EmptyPanel:dialog' in page '[Page class = org.hippoecm.frontend.PluginPage, id = 38, render count = 1]'. Perhaps the behavior did not properly implement getStatelessHint() and returned 'true' to indicate that it is stateless instead of returning 'false' to indicate that it is stateful.
INFO at org.apache.wicket.Behaviors.getBehaviorById(Behaviors.java:318) ~[wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.Component.getBehaviorById(Component.java:4601) ~[wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.core.request.handler.ListenerInterfaceRequestHandler.invokeListener(ListenerInterfaceRequestHandler.java:247) ~[wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.core.request.handler.ListenerInterfaceRequestHandler.respond(ListenerInterfaceRequestHandler.java:234) ~[wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:895) ~[wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64) ~[wicket-request-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:265) [wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:222) [wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:293) [wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:261) [wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:203) [wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:284) [wicket-core-7.14.0.jar:7.14.0]
INFO at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:9.0.30]
INFO at org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:58) [hippo-cms-login-14.1.0.jar:14.1.0]
INFO at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:9.0.30]
INFO at org.hippoecm.hst.core.container.FilterChainInvokingValve.invoke(FilterChainInvokingValve.java:72) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.JCRSessionStatefulConcurrencyValve.invoke(JCRSessionStatefulConcurrencyValve.java:56) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.SubjectBasedSessionValve.invoke(SubjectBasedSessionValve.java:58) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.SecurityValve.invoke(SecurityValve.java:177) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.LocalizationValve.invoke(LocalizationValve.java:101) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.CmsSecurityValve.invoke(CmsSecurityValve.java:60) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.InitializationValve.invoke(InitializationValve.java:40) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline$Invocation.invokeNext(HstSitePipeline.java:288) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline.invokeValves(HstSitePipeline.java:173) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstSitePipeline.invoke(HstSitePipeline.java:155) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.core.container.HstRequestProcessorImpl.processRequest(HstRequestProcessorImpl.java:81) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.container.HstDelegateeFilterBean.doFilter(HstDelegateeFilterBean.java:511) [hst-core-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.container.DelegatingFilter.doFilter(DelegatingFilter.java:68) [hst-commons-14.1.0.jar:14.1.0]
INFO at org.hippoecm.hst.container.HstFilter.doFilter(HstFilter.java:51) [hst-commons-14.1.0.jar:14.1.0]
INFO at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [catalina.jar:9.0.30]
INFO at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [catalina.jar:9.0.30]
INFO at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [catalina.jar:9.0.30]
INFO at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) [catalina.jar:9.0.30]
INFO at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [catalina.jar:9.0.30]
INFO at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [catalina.jar:9.0.30]
INFO at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) [tomcat-coyote.jar:9.0.30]
INFO at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-coyote.jar:9.0.30]
INFO at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) [tomcat-coyote.jar:9.0.30]
INFO at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1598) [tomcat-coyote.jar:9.0.30]
INFO at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-coyote.jar:9.0.30]
INFO at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_191]
INFO at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_191]
INFO at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:9.0.30]
INFO at java.lang.Thread.run(Thread.java:748) [?:1.8.0_191]
INFO

and later also

[DefaultExceptionMapper.mapUnexpectedExceptions:170] Unexpected error occurred INFO org.apache.wicket.core.request.handler.ComponentNotFoundException: Component 'root:pinger' has been removed from page.