By "goes idle", do you mean that the process goes down to 0% CPU usage, or that it disappears entirely? Do you run your clients hidden (-hide), or can you see what's happening from the front-end? Does it still toggle between showing #a and #b on the duallies?
The only thing I can say is that my FreeBSD SMP box has been untouched for months at a time in the recent past with no problems.