When the ace:dialog component generates one of the div's, the class list looks like this:
class="ace-dialogconfpopup ui-dialog-content ui-widget-content"
The "confpopup" text is the styleClass I specified, e.g.,
<ace:dialog ... styleClass="confpopup">
The bug is probably due to this code in org\icefaces\ace\component\dialog\Dialog.java (line 55):
static final String SHOW_CLASS = "ace-dialog" ;
static final String HIDE_CLASS = "ace-dialog-hidden "; /* (for comparison) */
Note that the hidden class ends with a blank, but the SHOW_CLASS does not.