Warnings about an 'Undetached JcrItemModel' when a document is saved with changes

Steps to reproduce:
1. start the GoGreen CMS with "mvn -Pcargo.run -Dcargo.jvm.args='-Dwicket.configuration=development'
2. login to the CMS as admin
3. open the document 'Hippo Go Green -> Events -> 2010 -> 12 -> NextGenFuels 2010'
4. add text in "summary" field and click on "save & close"

Expected behavior - Document should close with new changes getting highlighted without logging any errors
Actual behavior - Below logs are seen in the console (but the new changes are saved)