I haven't had problems with race conditions when running the same bot multiple times. But you have to be careful that there are no problems when running the bot twice on the same page in sequence either. That is, the second run should be a no-op, rather than accumulating more changes.
Yeah, I know about that issue. I'm usually careful to first do a run without changing anything, and then examine the output, which usually (but not always ...) helps, although I've still run into it occasionally ...
