Moving a Button located in an AnchorPane to a Tab content gets you NPE

Testcase attached. Although the test case look a corner case, this is a feature that we do offer in the SB. We allow the user to replace the content of a Tab containing an AnchorPane with the child of the AnchorPane.

Simply click on the button until you get the stack (should need 2 clicks).

Once we run into this issue the SB is stuck.