Wait, are you sure? I thought Armory dev posted up a bounty for message signing compatible with bitcoin-qt, which was completed?
https://bitcointalk.org/index.php?topic=179422.0I learned the hard way, and I'm sure frustrated Canary in doing so, that Armory does not digitally sign in a way that is compatible with the bitcoin-qt method, so make sure you don't sign it with Armory. (My understanding is that compatibility will come to Armory later)