errors logged when saving a document: WicketObjects.resolveClass():86] Could not resolve class [int]

1) Login as author/author
2) Go To The Documents
3) Go do a document, for example Hippo Duurzaam/Producten/Voedsel/2010/07/Berkenhouten composteerbaar bestek
-> Notice warnings (3)
4) Click Edit
5) Click Save
Expected: No warnings in the console log
Actual: Stacktrace (4) and more warnings (5)

(3)
[INFO] [talledLocalContainer] 08.08.2013 13:31:04 WARN [org.hippoecm.frontend.plugins.gotolink.GotolinkDocumentsShortcutPlugin$1.onClick():60] no focus service found
[INFO] [talledLocalContainer] 08.08.2013 13:32:32 WARN [org.hippoecm.frontend.model.JcrItemModel.writeObject():327] Undetached JcrItemModel /content/documents/hippogagroen/products/voedsel/2010/07/berkenhouten-composteerbaar-bestek/berkenhouten-composteerbaar-bestek/hippogogreen:categories
[INFO] [talledLocalContainer] 08.08.2013 13:32:32 WARN [org.hippoecm.frontend.model.JcrItemModel.writeObject():327] Undetached JcrItemModel /content/documents/hippogagroen/products/voedsel/2010/07/berkenhouten-composteerbaar-bestek/berkenhouten-composteerbaar-bestek

(4)
[INFO] [talledLocalContainer] 08.08.2013 13:23:37 WARN [org.apache.wicket.core.util.lang.WicketObjects.resolveClass():86] Could not resolve class [int]
[INFO] [talledLocalContainer] java.lang.ClassNotFoundException: int
[INFO] [talledLocalContainer] at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680)
[INFO] [talledLocalContainer] at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526)
[INFO] [talledLocalContainer] at org.hippoecm.frontend.Main$1.resolveClass(Main.java:151)
[INFO] [talledLocalContainer] at org.apache.wicket.core.util.lang.WicketObjects.resolveClass(WicketObjects.java:72)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.FormComponent.getType(FormComponent.java:830)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.FormComponent.convertInput(FormComponent.java:1181)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.AbstractTextComponent.convertInput(AbstractTextComponent.java:129)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.FormComponent.validate(FormComponent.java:1137)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form$16.validate(Form.java:1862)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form$ValidationVisitor.component(Form.java:177)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form$ValidationVisitor.component(Form.java:161)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:274)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrder(Visits.java:245)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.FormComponent.visitFormComponentsPostOrder(FormComponent.java:389)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form.visitFormComponentsPostOrder(Form.java:1093)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form.validateComponents(Form.java:1854)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form$17.component(Form.java:1968)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form$17.component(Form.java:1955)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:274)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrderHelper(Visits.java:262)
[INFO] [talledLocalContainer] at org.apache.wicket.util.visit.Visits.visitPostOrder(Visits.java:245)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form.validateNestedForms(Form.java:1954)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form.validate(Form.java:1818)
[INFO] [talledLocalContainer] at org.apache.wicket.markup.html.form.Form.process(Form.java:894)

(5)
[INFO] [talledLocalContainer] 08.08.2013 13:35:15 WARN [org.apache.wicket.ajax.XmlAjaxResponse.writeComponent():95] Component '[FeedbackPanel [Component id = feedback]]' with markupid: 'id2b0' not rendered because it was already removed from page