Yeah, when I hit that one key that is at the top of my keyboard that always closes the entire game out especially when multiplayer, sucks, can't even keybind out of Alt+f4 unless they added that in without me noticing in World of Warcraft. My old laptop had a key that did nothing at all except shut any game i was playing down faster than I do manually. That was it. Was next to my Delete key.
Could be worse, build mode could have a feature where you must save it before exiting out of it or it resets. But you lose nothing, just some irritation.
I have never used keys in build mode. My one thing for Sims has always been to keep my hands and everything else OFF of the keyboard.
On a serious note though, it sucks when your game gets shut off after spending a long and not yet complete session in CaS ^.^ That will get me to go find somewhere else to mind my business.