"Sync repository" fails w/o any indication why?!

When I try to sync my fork with the master (if you want to try: https://bitbucket.org/Marsu42/ml-mod6d) I'm getting the error message "Unable to merge - conflicts during merge". Problem is: even after resolving all issues with files marked with "conflict" in the diff, it still fails w/o any file marked as a problem - unlike the promised "View the conflicts".

I have encountered this problem multiple times by now and the only solution I found is to completely reset, i.e. delete the repo, re-fork and re-patch in all my changes. Is there any way to find out what the problem is?