The problems you describe are exactly what I experienced several months ago when I switched from using graphic buttons to using css buttons. Have you done that? It seems that there are some problems getting styles to work in forms cross-browser.

The css buttons included in the default Zen install is not the same as the CSS Buttons contribution (see Downloads). The latter will eliminate these issues for modern browsers, but not for extremely old browsers. I decided not to bother supporting the earliest of the 5.x series of IE or any old versions of Netscape. You may not have that option.

I can rreport that for all current browsers, and all versions of IE from 5.5 up, the CSS Buttons contrib works fine.

YMMV

Rob