Steps to reproduce:

1. User A makes changes to a File.
2. User B makes changes to same file.
3. User B does a pull this causes conflicts with the file.
4. User B right clicks file, uses external merge tool (in my case Perforce P4Merge), looks at the changes, decides actually not to make any changes and will accept the origin copy of file and so does:
   • Switches back to SourceTree on the little popup merge dialog click [Abort]
   • Switch back to P4Merge, close, don't save changes when prompted.
   • Switch back to SourceTree - BUG The file has been move to Staged list even though viewing the file shows there are still conflicts, unstaging, right click on file and now all the resolve conflict options are disabled. I aborted the task but yet it thinks it has been resolved, in my eyes this is a big bug. The preview of the file in SourceTree is not sufficient to make a decision, but because of this bug there is no way to stop once you've launch the external merge tool.