replaced cartridge in shower mixer (old one was dripping). Now when I pull the knob for water it ***** itself back in. After 3 or 4 times it stays on. Its a Moen, pull on, push off, twist for hot/cold.
What can I do?
Is it just new? Or do I have to live with it?
Thanks.

Sounds like a defective part. Change it. It should not go back in once pulled out unless you push it youself. Do not take the new one apart to see if you can fix it. Once you do this you will most likely own it.