Did FB 4.7 change how Embed() CSS directive works?

I'm new to Flash and am maintaining a site written in an earlier version of Flash Builder (don't know what version). Our only license is for 4.7 so I imported the project into 4.7 and built. Everything works fine except that a set of images that are supposed to fill in a close box, and are supposed to change based on mouse over and click, are not showing up at all.

The images are being embedded through a CSS file:

   upSkin: Embed(source="assets/tab/Close_Up.png");

   overSkin: Embed(source="assets/tab/Close_Over.png");

   downSkin: Embed(source="assets/tab/Close_Down.png");

}

I decompiled the old and new swfs with JPEXS Free Flash Decompiler and found that, in the old swf, the images are stored as images (DefineBitsLossless2) with names like:

ereviewer2__embed_css_assets_tab_Close_Up_png_491510569

In the new file, they are stored as sprites (DefineSprite) with names like:

_TitleWindowStyle_embed_css_Assets_swf_CloseButtonUp_931849471

The tabs are created with something called com.Extanded_TabNavigator.

The only difference between the two builds is the version of Flash Builder used.

Any insights into this problem?

Thanks