Having latest something does not mean "no problems guaranteed"
I have this tearing on a 280X and 14.4/14.7rcX drivers, so if we don't see any nvidia users complaining about this, it might be an issue with AMD cards indeed
Hmm, I've recently been using Windows 8.1, and have two AMD FirePros. Can't say I've noticed a similar issue, but I do get the occasional lines flashes for less than a split second on the right side of my screen.
Note, I'm running the monitor off of a Thunderbolt 2 port. I've no issues at all in OS X. I'm thinking it's just old AMD drivers really.