Ok, Thanks guys.
Psylence - thanks for posting that, sounds just like mine. So I guess mine is working ok.
I'm kind of surprised that this is an issue. IMO when the voice voice count / processing power is exceeded it should just cutoff the release of the oldest notes (aka voice stealing). I think that keeping tight timing should be the #1 priority. (And it's interesting that this (keeping the timing) is how it behaves when using TI or the arp).
I've used a lot of different synths over the years and this is the first time I can think of one whose timing is dependent on voice count. Pretty disappointed about that TBH.
Anyway, I've sent a message to Access support about it. Seems somewhat doubtful that they would (can?) do anything about it at this point though.