In addition to the “Better Transitions” there are “Show / Hide Transitions”. 

These Transitions are triggered when the option list of the dropdown is opened (Show) or closed (Hide).

 The same transition types as in “Better Transitions” are available.

As with the “Toggle Transitions” also the “Show / Hide Transitions” may behave unexpected when the same target and transition type is selected for a normal or “Better” Transition as well as for a “Show / Hide Transition”.