particular, it will keep not only objects referenced by your current set
of branches and tags, but also objects referenced by the index,
remote-tracking branches, refs saved by 'git filter-branch' in
-refs/original/, or reflogs (which may reference commits in branches
-that were later amended or rewound).
+refs/original/, reflogs (which may reference commits in branches
+that were later amended or rewound), and anything else in the refs/* namespace.
If you are expecting some objects to be deleted and they aren't, check
all of those locations and decide whether it makes sense in your case to
remove those references.