I was about to finish a big map (1080 x 1080) when the program closed...just like that.
I was right cliking/draging in floor mode to remove the extra tiles I didn't want in the map and BANG!! No more DC3

It's not the first time. An other time it closed when I mouse-scrolled to zoom in/out.
I also notice that when there are a lot of wall in a map. (like the one i was actualy doing, it as a strong tendency to lag. And trust me it's not my PC. Maybe the more info DC3 must manage the more risk there is for the program to shut down.

well it's just the same with me i spent an hour to draw a map, and it was almost done the program closed! i'm not complaining or anything but as you asked us to post about bugs i'm doing it