I just installed new update. For sure it wasn't the one with november's updates, because i got it on ~15th. The compilation number is 00WW_3_72A.
I quickly checked, and putting an app into bg, opening another one, and then switching back to the first one doesn't look like it's starting it as if it was killed. But maybe that's a reboot effect.
Could you check if you have the update pending and test after it's done?
Well, after these three days i can say that the issue still persists...
00WW_3_72A and five days of uptime here. The issue is fixed or at least patched to an acceptable level.