I searched the Korg forums for this topic and found the following thread.
http://www.korgforums.com/forum/phpBB2/viewtopic.php?t=21389&highlight=fill

According to what they say the issue is the instruments that play in the fill are not the same as the ones playing in the style, so if you do not hit it just right at the beginning of the measure then it sounds wrong.

That's what I'm going to listen for on my next try-out.

Graham

Graham