While playing SMP, the issue of redstone repeaters "locking up" (getting stuck in the on state) was brought up. Another user showed me their issue, a redstone clock using two repeaters and redstone wiring that was no longer "ticking". Breaking and replacing the offending repeater fixed the problem. They claimed that this issue was caused by unloading the chunks the repeater was in, while it was powered. Curious, I set about my own tests: a lever next to a repeater failed, multiple times, to create a "stuck" repeater; creating my own, identical, clock, also failed. Thus leading me to my question:
Under what circumstances will redstone repeaters become "stuck" in the on position (and if it only sometime occurs, what seems to be the probability)? (It may help to consider that this does not (to the best of my knowledge) occur in single player.) Information on fixes is also appreciated.