I've created some backport tickets to branch-3 (e.g.
HIVE-20181) and made the mistake of uploading the patch files with wrong filename (. instead of - between version and branch).
These get applied on master, where they're already present, since git apply with -3 won't fail if patch is already there. Tests are run on master instead of failing.
I think the patch application should fail if the patch is empty and branch selection logic should probably fail too if the patch name is malformed.