I've got the same problem, too (amongst others)! (Sapphire Radeon r7 260x)
When the screen turns black after closing a game, the system doesn't freeze though. I figured you can "fix" this, without having to reboot: I've got my computer screen connected to the DVI port and a hi-fi system connected to the HDMI port. So when the screen turns black, I turn on the hi-fi and the graphics card somehow displays a correct image. (should work with any second screen or hdmi device...)
Other problems I've encountered with my r7 260x:
- System crashes when music is played via HDMI (sound via HDMI works perfectly when in-game though)
- sound crackling
- horizontal lines flickering on screen
- memory clock stuck at 150mhz (thus, horrible lag in-game)
- "display driver stopped responding" error messages
I've read several threads about r7 260x problems, where people were complaining about some or all of these problems, too. Seems like it is actually a driver problem.
Did you receive a new r7 260x already? Are the problems gone?