Anh – I set up a new sample custom field section and added a few fields without the special field ‘Group’. looks like those entries work as expected… so without any deeper testing it looks like the ‘Group’ feature needs some additional work.
PS – the Group field type is very handy – so I’ll ask that you add it to your work queue and while you are at it – please consider adding a ‘DUPLICATE’ option to the Group field so we can duplicate entire field sections. Also – making it work with Beaver Themer will be a nice option too!!