Response from the site administrator
jasonsilver, 29.11.2011
OK, there is definitely a bug there-- I will begin tracking it down and let you know when it's finished.
UPDATE:
I found the problem... if you add a person to a group, but don't give them a role within that group, then they will not be scheduled.
So you must actually give group members a role of some sort.
If a role is not intuitively necessary for the group in question, for example if the group is a children's choir that doesn't necessarily have assigned parts (soprano, alto, tenor and bass are not relevant), then create a placeholder to use (such as vocalist in this instance).
If the group is a drama troupe, you might consider naming them all actors.
If the group was an elder board, you might consider naming them all participants.
I hope this clarifies the problem and is a good enough solution.
I have added a warming on the groups page that you must assign roles to your groups.