Flex：当滚动条出现时，Panel容器会丢失borderSkin（嵌入式swf）

I've been asking around and googling like crazy, but can't figure this one out. I have a panel in a flex-AIR app with a borderSkin - an @Embed swf symbol. Everything looks good till the panel has enough children added to merit a scrollbar, at which point the borderSkin disappears, leaving only the default background color. Remove the children and the borderskin comes back. The swf symbol uses scale9 grids.I've been asking around and googling like crazy