Branches on remotes (on Stash or otherwise) remain visible forever. Remotely deleted branches will never dissappear. This is confusing for developer, because it looks like a remote branche still exists, but when trying to switch to one and execute a pull, you'll get an error saying the branche no longer exists on the remote.

Please remove branches from the GUI when they no longer exist on the remote.

Seems like a reasonably high priority issue to me, since this is corrupting the development workflow, most notably when working in feature-branches.