Oh, I see what you mean .. I vaguely remember having that problem myself. Let me double check on some of my more recent screen shots.
Ah yep, thats what I remembered about it. I suspect the group number is there but it is being overwritten by a buff/debuff icon. In all my screenshots I have those icons as we always do ICC which gives you an auto buff/debuff.
If Scott is displaying the group number at it is being overwritten maybe it needs to be moved to the left of the name so that it is always visible
