When you want to grant multiple permission sets from the User Group Permissions Sets page (User Group Permission Sets (9834, List) you are allowed to push on "Select More", but when you select more and push OK - it only puts in the last selected permission set and not all the selected Permission sets.

I do know the page (Permission Set by User Group (9837, Worksheet) and this works fine for me, but for the end users, this overview gets confusing and they simply give up on the task to grant permission sets themselves and hands it over to us as partners - and that is of course business, but I really think you should support the above mentioned function when you actually show the button/action.