Envision a scenario where a friends' party wipes. You log in to go and rescue them on your high level character. Unknown to you at the time, your new character picked up your friends' weapons weeks prior after a low level dungeon went poorly. When you go do the rescue, you set off the muling script, even though you're not muling.
This scenario happens way more frequently than you'd think.
This seems to be a currently gray area. I know it happens, and I know I would do it (and would want someone to do it for me), but I also have seen indications that it's frowned upon because it can be very OOC. It's specifically against the rules to use your own PC to rescue another of your PCs, isn't it? Asking a friend to log in and rescue you seems to be in the same spirit, if not the same in execution. That a friend can rescue you but not your weapon makes the party wipe have a more serious consequence
(Please don't interpret the above as a request that such rescues be outlawed; I like it the way it is and being able to help other PCs helps balance the inevitable conflicts among us.)
My personal preference, though, would be to enforce rules through mechanics whenever possible so as to avoid requiring DM intervention and punishment. As a player, I don't like being fussed at; if I were a DM, having to fuss at players would seem to be one of the least enjoyable parts of the job. It takes away from the time DMs can spend doing more creative and fun things for players.
When Arawn wrote the following, I thought it expressed a similar weariness with the number of times DMs were having to make these calls:
Please, we're all here to play. Just following the rules isn't too much to ask.