WPF loves to divide by zero

Ignoring for a moment how worthless the WPF designer is ( and I've not tried the VS2010 one b/c VS2010 is so slow and buggy that I don't want to move my projects there ), it seems like at random points, my large WPF project will compile, and fail to run, with a divide by zero error at the root of the project, in the App class. Rebuilding will fix it, there's never a bug in my code.