alt tabbing when paused game cancels the app overall?

[Chronosphere]

so am curious i paused my sp game right and alt tabbed to the forums, 1min and suddenly game exited itself, is this a failsafe or something cuz kinda wierd, is my medium rig not able to hold it up in the background or something?

 

[SylenThunder]

A log from that session would be helpful. Most likely the d3d driver crashed.