Deleting a component from the channel manager leads to error in iframe

Reproduction:

1) log on to demo http://cms.demo.test.onehippo.com/
2) Go to channels perspective, select channel, enter edit mode
3) Add a component to a container, and delete it again, confirm that you want to delete

Expected: component is successfully deleted
Actual: component is deleted, but an error message pops up.

Reproduced locally with an archetype-project.