Moen shower/tub valve leaking from stem when water is on

Hi there. I've got an old Moen single handle tub/shower valve that leaks from the stem only when the water is turned on, so the water runs out of the stem, into the sleeve, and into the tub (and some of it goes back into the wall through the sleeve I assume). I haven't pulled the cartridge, but I'm assuming it's a 1200 or 1225.

There is a hole in the stem (you can see the hole in the picture I've attached), and this is what the water is coming out of.



Is this a faulty cartridge or is this normal?

Thanks.