Currently it is counterintuitive that doubleclicking an element in left/right CTweenBox lists doesn't actually move that element to the other list.

Usecase example, host configuration page: quite often I need to add/remove only one group from host's groups list, and I want to do it quickly, without having to select the group I want to add/remove, and then moving the mouse pointer over "<<" or ">>" buttons. Doubleclicking a group should be enough to move it to the other list.