Taskbar 'pinned' to sidebar and won't unpin

Since my InDesign updated this morning (can't say for definite that this is connected, but hadn't noticed it before) my contextual taskbar is now 'stuck' onto the right-hand sidebar.  It's not as though it's pinned, as such, as it will move up and down, but is locked into it's horizontal position.  Clicking 'unpin' does nothing; if I hide it and then open again it reappears in the same position, in the same state.

Any ideas on how to solve this ?