The behavior you describe can occur with "filled curve" if the curve you draw touches the edge of the image slice -- the wrong fill region might be computed if this happens. I've never seen what you describe happen under other circumstances, and haven't been able to reproduce it here.
The Draw Dataset plugin was recently upgraded, but I don't think anything I did would have these effects -- the changes were to let you associate a label with each drawing value. The actual drawing hasn't been changed recently.
bob cox
