On this moment group "Custom groups" have strange appearance. When you click any group -- you can see content of this group but when you click on "Custom groups" you see content of previously selected group. Even "All torrents" group have something to show but "Custom group" can't show anything.
I propose to combine "Ungrouped torrents" group with "Custom groups" to eliminate one useless group. Resulting group should contain all user-groups and will show ungrouped torrents when selected. I don't know which name discribe this group properly, maybe someone suggest something? E.g., "Groupable torrents".