On Desktop, you can see what you are selecting like so:
But on mobile, you can't really see what you are selecting. Here is an example:
I'm not sure if this is a bug, but I wonder if it can be improved for the touch experience?
Open the Smilies dropdown and then select another icon from the toolbar that includes a dropdown. It opens the new dropdown but the Smilies dropdown doesn't go away. It works just fine with toolbar icons with no dropdown.