Best practice dictates that dropdowns open on mousedown, such that that user can press, move to the desired item, and release all in one movement. You'll of course find this behaviour across many apps and OS's, including MS Office, Windows and OSX. Sadly, Kendo UI dropdowns open on mouseup/click, rather than mousedown, which means the user has to do two clicks to get to what they want. For heavy-usage applications, this is a big pain for users, and definitely affects usability.