Marked for the PM to review.
Seems to work fine on my install. After choosing single group limitation, then selecting the group, it returns me to the account settings page, which is what I would expect. Were you adding the limitation to an orion account a windows account or a windows group?
Sorry it took me so long to get back, but I am using a domain group (lower case 3 letters)\#(mix of upper lower and spaces), I tried it with another similar group and it does the same thing.
Check box group, Click Edit, Click "add limitaion", set radio button to "Single Group", Click "Continue", use drop down to select group, click "submit", return to radio button dialog where I can select "Single group" again.