My event is set with a minimum group of 4 and a max group of 4 to force only groups of 4 people. I am using Detailed Group Registration type.
When I fill out member 1 and then click on the add next member button. It takes me to Member 2 form. BUT if I click the CANCEL MEMBER button at the bottom, it takes me straight to the billing page to check out which I can. 1/4 of my registrations are coming through as singles. There seems to be a loophole when clicking on cancel member that overwrites the Min/Max Group Member rules.