Gmail valid signature

As far as I'm concerned, it shouldn't pick up my signature and say it's valid, seeing as the email isn't from me (but my signature is in the quoted text). Is it possible for it to only check if the signature is above the "Show quoted text"? It seems to just pick up the first signature in the email even though it's from several emails prior. If I send the email without rich text formatting, it works fine and doesn't detect it (because of all the >s).

I'm using Fx 3.0.1 and it does this on XP and Vista. =)