Intermittent issue with "sync now" on Mercurial branches causing path corruption (BB-10051)

This has happened twice, with two unique branches from 'default' on one of my repositories. When using the "sync now" feature to update each branch from default, the request completes, however I'm unable to pull down / checkout the updated branch.

Mercurial prints an error similar to the following:
abort: No such file or directory: /path/to/my/working/copy//some_directory/some_file.ext

Notice the insertion of a double slash (//) in the path...

When this happens, it appears to render the branch useless because it fails to checkout on any platform without throwing that error.

Merging default into a branch with SourceTree or Mercurial CLI works fine...and this is what I've done to work around the issue...creating a fresh branch from a previous commit, and merging with SourceTree.