deletion of branch seems to modify tag as well?

$ git push origin :ABRANCHNAME
remote: Firing Pre - receive hook
remote:
remote:
remote: Firing Post receive hook
remote:
remote: Branch is ABRANCHNAME -- not creating Trigger file since this is not _int branch
remote: error: Trying to write ref refs/tags/ABRANCHNAME!SN-BL-20130605_100513_04363 with nonexistent object 0000000000000000000000000000000000000000
remote: fatal: refs/tags/ABRANCHNAME!SN-BL-20130605_100513_04363: cannot update the ref
To ssh://git@ourgitserver/repositoryname.git
- [deleted] ABRANCHNAME


I would not expect this behavior.  Is git attempting to modify the tags associated to the HEAD commit on the branch in addition to the branch?   If so, I would like to consider this a bug report...



Thanks,

Roy Lyons