Basically, if you hit on the 'one' (but NEVER fractionally late) or on the 'four' (or later) on a Korg, you don't actually get any glitches, because you are doing the ONE thing that the Korg wants to see...

On the 'four' it waits till the 'one' to bring in the fill, and as long as you don't hit the 'one' late, that triggers the fill with no overlap with the previous bar (which is what everyone is hearing).

But many use fills either less precisely, or more often, partially. In other words, fills can be used for MUCH more than simply triggering the entire fill. Hit the fill on the 'two' or the 'three', or even the 'four' (but not late into it) and you get what is called a 'pickup' rather than a fill, a 'lift' in feel without the drama of an entire bar's fill.

This is a VERY common drummer technique.

Now, I know some of the Korg fans are going to chime in here about the Korg's extra long variations, that have pickups at four bar boundaries, and this is all well and good. BUT... some songs don't have regular 8 bar repeated sections, and sometimes you need a pickup on other bars.

THIS is what the Korg has a problem with, depending on the style. You simply can't do your own pickups without things getting unpredictable.

Bend what YOU want to do to what the Korg will let you, and all is fine, but personally, I'd rather the arranger do what I want than the other way around...