How can I make clientside findareanpcs work reliably?

[Tyhm]

(I had posted all this, then it fixed itself for a bit, now it's broken again.)

Problem: See picture. The player's weapon:

PHP Code:

     if(player.chat=="") player.chat = (area_npcs.size() SPC "npcs in area (" @ temp.lowestx @ ", " @ temp.lowesty  @ ", " @ temp.highestx  @ ", " @ temp.highesty @")"); 


And the NPCs have a fairly predictable "message your location and timevar";
the trouble is they keep updating the message - even with the timevar - serverside and clientside, no problem - but after they've been idling against a wall for long enough (hard to pin down exactly how long it needs to be; could be a few minutes, could be until a player re-enters the map, could be until a player re-logs, whatever) they Fall Off the findareanpcs results table.

Until the player makes them move. Then they're back in the detection area.

So do I just have to make the zombies move around every so often? :-P