I also suspect that it is something in css or class.
However if I cant find the error I'll be back here for help
<{if $xoops_banner and $xoops_banner != ' '}>
<{includeq file="$theme_name/xobanner_commercial.html"}>
<{else}>
<{includeq file="$theme_name/xobanner.html"}>
<{/if}>