Correct me if I'm wrong : I do believe that the admins of groups were recently able to set the limit ( thanks to Sean ) and with that, folks who over submit that number, the overage is simply rejected and won't go into the pending pool.
When a picture is rejected in this manner, you have to go back to the beginning: for submitting it to the group/s.
You may have to delete the check mark for the group, SUBMIT that, and then re-check ( choose ) the group / s to which you want it posted ( those from which the picture was rejected in this manner, and re- submit that change.