This is in fact normal Windows behaviour. A combo dropdown will always be sized to as many lines as there are items up to a MAXIMUM of the height you specify. In that sense, the height dialog option specifies a max height, not an absolute height. There is no way that I know of to set the actual height of a drop down combo. You should actually see this behaviour with any dropdown combo with a hsbar in Windows. Drop-downs are not meant for horizontal scrolls, however, so you won't see this often.
