Channel manager blank when running in Wicket debug mode

If you start the CMS as follows:
$> mvn -P cargo.run -Dcargo.jvm.args='-Dwicket.configuration=development'
then the channel manager sometimes turns blank and does not work anymore.

Steps to reproduce (in archetype)

• log in and go to channel manager
• open "Getting started" channel
• click "Edit channel"
• drag the Wicket logger console down a bit so that you can see the buttons.
• click "Channel settings" at the right-hand side and close it again
• close the lightbox by clicking the X icon
• click "Channel settings" again
  Expected: channel settings opens again
  Actual: the channel manager turns blank and becomes unusable.

The only way to recover is by logging out en in again.