Text box cuts off top of text

When I use larger fonts in a text box (PPT 2000 or XP), the top of the text is sometimes cut off. If I try to enlarge the text box height to accomodate the large font, it looks like it's resizing, but when I release the mouse, the text box is only moved upward, not resized.

This happens intermittantly - a text box will behave when first created, then for no reason will suddenly begin chopping off the text. Sometimes it starts when I add animation to the box.

Any Ideas?