I agree this looks like a WindowServer issue. Just had it happen after locking and then unlocking the screen (no sleep involved), but I don't see any log messages about VRAM.
Here's my log if it offeres anyone any clues (the messages form Colloquy, which was the affected app, about all disaplays reporting they are mirrors seem potentially relevant):
1/9/14 6:23:26.831 AM loginwindow[23701]: Login Window - Returned from Security Agent
1/9/14 6:23:26.896 AM WindowServer[97]: Session 259 released (1 references)
1/9/14 6:23:26.901 AM WindowServer[97]: Session 256 is switching to console
1/9/14 6:23:26.910 AM WindowServer[97]: Session 256 retained (2 references)
1/9/14 6:23:26.911 AM WindowServer[97]: Session 259 released (0 references)
1/9/14 6:23:26.917 AM loginwindow[23701]: CGError CGSGetDisplaySystemState(uint64_t, CGSDisplaySystemState **): MIG error 0xfffffecc: (ipc/mig) server died
1/9/14 6:23:26.926 AM loginwindow[23701]: CGError CGSGetDisplaySystemState(uint64_t, CGSDisplaySystemState **): MIG error 0xfffffecc: (ipc/mig) server died
1/9/14 6:23:26.929 AM loginwindow[23701]: CGError CGSGetDisplaySystemState(uint64_t, CGSDisplaySystemState **): MIG error 0xfffffecc: (ipc/mig) server died
1/9/14 6:23:26.929 AM loginwindow[23701]: CGError CGSGetDisplaySystemState(uint64_t, CGSDisplaySystemState **): MIG error 0xfffffecc: (ipc/mig) server died
1/9/14 6:23:27.000 AM kernel[0]: **** [IOBluetoothHostControllerUSBTransport][SuspendDevice] -- Resume -- suspendDeviceCallResult = 0x0000 (kIOReturnSuccess) -- 0x2400 ****
1/9/14 6:23:27.084 AM WindowServer[97]: run_timer_pass: Session 259 is defunct for callback to 0x7fff884ed2d1
1/9/14 6:23:27.085 AM WindowServer[97]: run_timer_pass: Session 259 is defunct for callback to 0x7fff8833cd9a
1/9/14 6:23:27.097 AM Colloquy[23027]: All available displays report that they are mirrors. This seems wrong. Please comment in <rdar://problem/14731307> if you see this log
1/9/14 6:23:28.118 AM WindowServer[97]: disable_update_timeout: UI updates were forcibly disabled by application "Colloquy" for over 1.00 seconds. Server has re-enabled them.
1/9/14 6:23:28.326 AM WindowServer[97]: common_reenable_update: UI updates were finally reenabled by application "Colloquy" after 1.22 seconds (server forcibly re-enabled them after 1.02 seconds)
1/9/14 6:23:28.328 AM Colloquy[23027]: All available displays report that they are mirrors. This seems wrong. Please comment in <rdar://problem/14731307> if you see this log
1/9/14 6:23:28.404 AM Colloquy[23027]: All available displays report that they are mirrors. This seems wrong. Please comment in <rdar://problem/14731307> if you see this log
1/9/14 6:23:28.426 AM parentalcontrolsd[23736]: StartObservingFSEvents [849:] -- *** StartObservingFSEvents started event stream
1/9/14 6:23:28.908 AM WindowServer[97]: run_timer_pass: Session 259 is defunct for callback to 0x7fff882c6591
1/9/14 6:23:28.978 AM WindowServer[97]: **DMPROXY** (2) Found `/System/Library/CoreServices/DMProxy'.
1/9/14 6:23:29.021 AM WindowServer[97]: Display 0x04273380: Unit 0; ColorProfile { 3, "Color LCD"}; TransferTable (256, 12)
1/9/14 6:23:29.718 AM WindowServer[97]: run_timer_pass: Session 259 is defunct for callback to 0x7fff8833bf67
1/9/14 6:23:29.719 AM WindowServer[97]: run_timer_pass: Session 259 is defunct for callback to 0x7fff8833bf67
1/9/14 6:23:29.719 AM WindowServer[97]: run_timer_pass: Session 259 is defunct for callback to 0x7fff8833bf67