Sorry for not being a crossfire guru I have SLI lol, but I'll assist all I can
Is the corruption you speak of similar to the image tearing experienced when not having V-sync enabled (a screenshot would be handy)? Do you have Catalyst AI enabled or disabled? Of course you realise that certain games wont work in crossfire if AI isnt enabled and reverts to single card mode.
What monitor are you using - CRT's are having problems with crossfire, by switching to a TFT via DVI input it may solve the problem, that could be a video bandwidth issue although this is purely speculative.
What BIOS version are you running?
I've listed a link for you that may be useful: