Why does git-describe warn about something that you can't control?

On the perl.git repo if I use git-describe --all on some commits I get warnings like this:

$ git describe --all 3417e4f8422bcf13f799ce1acef44b27ccbef3d8 warning: tag 'perl-5.005_04' is really 'tags/perl-5.005_04' here perl-5.005_04

Except there doesnt seem to be any explanation for why the warning is being produced (it almost, but not quite looks random for the commits im looking at), how to silence it, or how to force git-describe to for instance use "tags/perl-5.8.0" instead so the warning is not generated.

I think this behaviour is confusing, either the warning should go away, or it should be improved and complemented by a switch to force git-describe to use the qualified tagname instead, or at the very least a switch to silence the warning (which is really annoying when you are doing git-describe on hundreds of commits in a go).

Details for the perl repo are in my signature.

Yves