I've got an R9 380 (Sapphire Nitro, FWIW.) with two monitors - 1920x1200 main (on DisplayPort), and a 1920x1080 secondary monitor (DisplayPort->DVI adapter) on the right, running Win7 64-bit.
When the PC re-enables the displays after power save kicks in, the main monitor is duplicated (mostly, anyways) on the second monitor. Windows still thinks it's a seperate monitor - windows opened on the second monitor still go there, but can't be seen until I run a fullscreen app on the primary monitor and then exit, at which point the primary and secondaries happily redraw what they were supposed to and things are normal again.
Possibly related - if I unplug the main monitor when it's running, Catalyst won't find it when I plug it back in.
Has anyone else run into this?