If I create a script but make an error in it, or if I start and then stop it, the next click on "Start" has no effect (though the "Start" button goes shadowed, as if the script has really started). That behavior really disappointed me - I kept closing and reopening the BTrace window for my app - until I discovered that I can achieve the same effect by just closing the "Output" part of the BTrace window. Anyway, clicking on Start should consistently lead to recompiling and restarting the script.