Donny, very few would be a better explanation.
Well at least in my experience anyway, (and Zuki's obviously).
Truth is if this were the issue that has been implied, it would be all over the Korg forums, as a major "must-do" update for Korg.
I believe most if not all the Korg forum members are quite silent about this supposed "issue", and they too seem to have no problems.
Also you can hit the fill in the middle of the bar to get a simple 2 beat fill if you want, and as you would also know, you can double hit the fill to have it repeat, same with the intros and the break button. the last one (break) I found very useful at times, particularly with those breaks that just have a stab on the first beat.
So a claim that you HAVE to hit fills only on the downbeat is also erroneous.
Dennis