Problem signing a tag

Nobody on the git IRC channel responded to this question, even after asking it a few times, so I thought I'd try here.

I'm having trouble signing a tag.  I'm using this command:

git tag -u EAFD344D14EA086E -F .git/TAG_EDITMSG tag_name

I type in my passphrase, and am then told:

error: gpg failed to sign the tag error: unable to sign the tag

However, if I use this command:

gpg -s -u EAFD344D14EA086E

and use the same passphrase, it works fine. Is there any way to find out why a key-signing is failing?

This is git 1.6.5.2 and gpg 1.4.9

Thanks!

j