How are long dropdownlists (combo boxes) in edit- and admin-mode supposed to work?

We have dropdownlists containing so many items that they cover the complete browser window height, from top to bottom. In fact, they are so long that we can't select the options at the bottom. There's no possibility to scroll down either.

If I'm correct, the dropdownlists in edit- and admin-mode are based on Dojo/Dijit. If they'd been based on the ordinary HTML select-tag there shouldn't have been a problem.