You may want to go and have a look at this discussion, in another forum, by Chris Kenniberg, it's called 3 Ways to Stop Blended Learning In its Tracks.
The comments there are useful for discussion on how you may be able to approach people who complain about how they do the wrong thing. They blame their tools, Moodle, rather than accept responsibility for their errors and learn how to do it better. I know, I am being very harsh here, but I would expect that their courses are their responsibility, and it is up to them to make sure it works properly. If you are using Weekly Format, then an end date is almost mandatory, I have not run into this problem before, mainly because people work out their timings beforehand using a calendar, I suspect.