As you work in LiveCode and start new stacks, save and close other previously opened stacks, as they can still be occupying memory. Sometimes you can get into a confused state where you're making a new untitled stack, only to find that there's already an untitled stack on the go, which you're asked if you want to purge. So why not treat yourself to a quit and fresh launch of LiveCode!
MGTestBed, and save it somewhere you can easily find. Perhaps in the folder with the
LCTestBedstack, which was feeling lonely!