Had Korg i3 & i30 for 6 years and no delays experienced at all on styles following a fill. My present Roland EM2000 certainly has not delays with all the built in styles or the 400 or so loaded from Zip Drive.
I play friends PSR9000, KN6000, PR903, VA7 and again no delays from fills to style.

Its definitely a problem I feel should not be there on any board.

Graham UK