No need to apologise, it's good to know that it's happening to other people!
Well, not good, but doesn't make me feel like I'm doing something daft to the system.
I've since discovered (about 20 minutes ago) that it is happening in multiple courses and groups for us as well, it's just that most staff were just shrugging and replacing the students in the groups and not complaining to me.
If you figure it out or hear anything elsewhere please do add it on here as I'm sure we can't be the only ones.
Derek