The combobox control doesn't resize properly when its container is scaled down or up.
If you put a combobox in a scaled movieclip, when you click on the combo its dropdown list doesn't scale accordingly to the movieclip.

Try my combo class and see what you can achieve (below)

When you use my special combo feel free to put it
in a nother movie container, scale it down or up and see the result.
To fix this use my class instead of the Combo that comes from Adobe
Download it here

