ComboBox with many records overflows page

[ferr]

I have a combo box with a thousand or so records, when the user opens the combo box, the list exapands normally (default maxHeight of 300px, so it looks perfectly fine), except that the window is suddenly overflown and the vertical scroll bar pops up for the page. This also bumps over some of my elements causing a rendering issue until they are "re-rendered" (i.e. the far right of my grid has half of the "Displaying Documents 1 - 20 of 2,000" cut off, if I refresh the grid it is no longer cut off).

How can I prevent this overflow without disabling overflow via css and without resorting to paging in the combo box?

edit: Happens in IE6 and FF2

edit: I guess I should note that the rendering issue is caused by the fact that my grid is within a div which has width set to a certain percentage of the page, so this rendering issue is not exclusive to this combo box issue, it will show up any time scroll bars suddenly appear. Though if I resize the page to cause the scroll bars to pop up the grid automatically corrects this rendering issue immediately..