[flexcoders] MX scrollbar with spark skin display issue

[method_air]

There is a gap between the thumb and the down button in the bottom position of 
an mx vscrollbar,  as seen here:

http://imgur.com/46eKt

...when using spark skins (css properties thumbSkin, up-arrow-skin, 
down-arrow-skin and track-skin),

Any ideas on how to fix it?

Thanks,

Philip