Hi,
Hm, yes, that looks like a Javascript/CSS error of some kind.
A multiple-instance filter sounds too hard to implement, I'm guessing...
By the way, questions about Semantic Drilldown should usually be sent to the SMW users mailing list - it used to be that this list was also for Semantic Drilldown and Semantic Google Maps and possibly some others, but at this point all of those extensions should be on the SMW users list.
-Yaron