Chunks unloading too fast? - plates and buttons messing up

I've done some searching around, but I can't seem to find any clues on this.

I've put on my map a few command blocks to enable quick teleporting between various regions. Those can be triggered using pressure plates and buttons. I've tested the mecanism, and it works. HOWEVER! Sometimes, the pressure plate or button will be stuck: if you've teleported away, come back to your starting point and try it again, the plate/button is stuck in it's "pushed" configuration and won't activate again. The only way to fix it is to destroy the plate/button and place it again. This happens often enough to be a major annoyance. Has anyone seen this behavior before?

My guess is that, since the teleports are far from each other, the source chunk gets unloaded from memory right after the user jump, before the plate/button has the to return to it's starting position. As such, the next time the chunk gets loaded, it remains in the pushed position until it gets replaced. If that's really what happens, an easy fix would be to slow down chunk unloading by, say, 5 seconds. That'd be enough to avoid the issue without causing any noticeable server load. Is someone aware of a server setting or mod to do this?

Using levers instead of plates and buttons do the job, but for esthetic and convenience purposes, I don't want to use them. Does anyone have a workaround to offer?

All this has been noticed with the latest recommended build (1.4.7-R1.0) on a Linux server with 1 GB of RAM.