We have an existing set of repositories, and now when we attempt to finish off feature branches in the tree, the dialog pops up with a small merge tree, drop down, and ok/cancel, and nothing useful is selectable.  This also happens if coming in via the hg flow button in the toolbar and clicking on "Finish Feature".

This was working fine in earlier version.

The dropdown and OK button are inactive, and the merge tree doesn't appear to be populated.   The window flickers briefly on appearance, and then reverts to this "dead state" shown in the capture attached.