Is the label in question rendering as a span, or as a label element? If it's a span, take a look at this and see if it applies in your case:
http://devnet.kentico.com/forums?forumid=60&threadid=26365
I just wasted over an hour trying to figure out what was going on here. This is a perfect example of the lack of sufficient documentation for Kentico. I couldn't find this documented anywhere.