dhtmlxCombo - problem with z-index in IE6

Dear Sir,
the problem still persist even after I tried to increasethe z-index, and even after using the latest version of"dhtmlxcombo.js".
Please, can you look at my site, so that you can watch it yourself? Use the following login:
username: ######
password: ######
After the succesful login click on the green “J - clanek v odbornem casopise”. You should be redirected on the following page:
##################
Now there are 3 combo boxes. Click on the one at the bottom called “Zeme vydani”. You will see my problem!
PS: Use Internet Explorer 6 !!! (in IE7 and Firefox there is no problem with it).
Yours sincerely,
Marcel Golias.

Issue caused by changing the default height of list element, while it change the heigh correctly, it block the built in workaround for “select” bug in IE.
To resolve issue add next line to exsting code

a.DOMlist.style.height=“SOMEpx”;
if (a.DOMlistF) a.DOMlistF.style.height=“SOMEpx”;