Vista bug - Playing sound in lump menu.

When selecting a lump in the lump list menu, it plays whatever is allocated to "Default Beep". It seems to do this for every type of lump. Markers, Maps, Graphics, etc. It does this when pressing up/down, or when selecting with the mouse. Now here's the odd thing. It's very erratic about playing the sound. It will sometimes do this if you pick just one lump. Other times, it will do this after picking a few lumps. And other times, it will only do it if up/down is held (which it will always play the sound with).