CMS breaks when opened in two tabs of the same browser

I thought it was not possible to be logged in to the CMS twice with the same user, but it seems to be now. It may be that this functionality has to be restored, or otherwise the described bug should be fixed.

Reproduction path:

• build a Hippo 11.0.2 project and install the essentials News feature.
• rebuild & restart
• log into the cms and browse to a news document: the URL changes to something like http://localhost:8080/cms/?1&path=/content/documents/myhippoproject/news/2016/09/the-medusa-news
• open a second tab in the same browser window, and request the same URL there
• go back to the first tab and wait for the pinger to refresh the screen or refresh it yourself manually. Result: broken CMS layout, see the screenshot.

Impressive stacktraces in the log too, like:

[INFO] [talledLocalContainer] 26.09.2016 10:27:33 WARN http-nio-8080-exec-8 [NodeUsageEvent.<init>:40] Error retrieving node identifier
[INFO] [talledLocalContainer] javax.jcr.ItemNotFoundException: Root node doesn't have a parent
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.NodeImpl$6.perform(NodeImpl.java:1754)
... etc...

I see this happening in Firefox and Safari, so it doesn't seem to be browser related.