That is indeed strange. My PA2X has non of that, just a natural decay or reverb after the one of the 3 endings stops. The effects and reverb for the lead parts and the arranger parts are separate though. Could it be that the reverb for the arranger parts was (accidentally) set to 0 on the Singe Touch Settings (STS) on some of the styles you played? The factory STS's can be overwritten by you own preferences, so this could be the case.

My advice: select a factory performance setting and check again. Even better: restore the factory settings, or "musical resources" as Korg calls them. Be careful because this action overwrites the user performances. So Don has to backup the user performances or STS's he wants to keep.