It´s as you write in your first sentence. I tried all different settings. There are two alternatives as long as i can see:
- different assignments för different groups (with different dates)
- delete the "until date" under "restrict access" and use "due date" under "availability" instead
My teacher changed to alternative 2. The different groups have to submit with a week interval. Due date is set to the second groups date.
good luck with reinstalling