Corrupted debugger layout

My debugger layout has become corrupted. For C++ debugging I cannot resize the bottom pane and I cannot access the debug controls. For QML debugging, the bottom pane has a different layout and is fine but there are two copies of the Expressions pane, one inaccessible and no Locals pane.

See attached screenshots.

This problem has persisted since I have migrated to Qt Creator 8.0.2.

My most pressing question is how to reset the layout as a workaround as this is unworkable. Then I'm happy to leave it to you to work out how it went wrong in the first place.

NB: I tried asking a question on Qt Forums but had no response for over 2 weeks.