For years the fills and variation changes on Korgs seemed "jumpy," i.e., they sounded abrupt with sudden changes in volume. Some folks like John Smies who used to post on this forum went through and edited all of the musical resources.

What I noticed is that new styles introduced contemporary with the Pa900 seemed smoother with fills and variation changes that were better integrated. If the EK-50 is using legacy resources from the PA50 / PA80 or "Triton" engine, it might be something you'll have to live with. As an entry-level arranger, re-using old software and hardware is one way to keep the price down, but you get only what you're paying for. My $.02.