New cartridge in. Why does the shower still drip?

[Panaplex]

Just put in a brand new Moen shower cartridge and put the tap (single lever) back on. Its in the "off" position but still drips. Why?

 

[ShaunCorbs]

Could be the body has a defect / split in the face / mating surface etc so the water is bypassing the cartridge or could be a bad cartridge

 

[Panaplex]

Could be the body has a defect / split in the face / mating surface etc so the water is bypassing the cartridge or could be a bad cartridge

Thanks. If the cartridge is not the problem, is there anything else that could cause the constant drip?