I know this is an old question but I find many have this problem so I am going to stick my nose into it. I had the same problem and in the DOT formums I found the following and it worked wonderfully
My fix should work flawlessly and just the way you want it to be. Either that or you can just add a reset for one in each room, make it so there's a max of 1 in the room and make it sentinel so it can't move around, that's all fairly easy and doesn't require any coding.
That happened to me a while back. I think the admins on Blood Moon (whose address I have forgotten) have worked out the way to fix it. You could connect to that and ask around.
You could always go into either update.c or move_char and have it check if there is another being in the room that they are about to move into. If there is then just have it return so they don't move.
sometimes when i or a player create a new character and say "say beginner" to the newbie guide - more than 1 being of light is there. hence asking the same question over and over. totally spam lol
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