The interesting part (to me) - is that regardless of the cause of this issue - it is likely that there are other (maybe many other) applications out there that could "benefit" from running on only a single core.
The server favors synchronized blocks to the use of volatiles (i.e. Atomics) at the moment. I tend to play things conservative until time that I find a problem or see an obvious opportunity. And, I hope I can say I'm not "over synchronizing" but I did synchronize as often as I determined it was needed (modulo the normal issues for humans not being very good at that).
Again however, even if the server is written in any silly manner you can imagine. The idea still seems to expose a an issue (and roundabout solution) I've never heard of before.