For everyone who's ALLEGEDLY "never seen that before"...I have...today.
I don't know how to upload a picture but there are lots of articles about paint not sticking to drywall all over the Web. In this case it's Glidden Premier interior exterior paint on drywall mud...week old, sanded and washed, dry...drywall mud.
It's true. Paint it on, peel the tape, and a whole sheet of paint comes off with it like a big rubber sheet.
Now I have to peel a whole wall of paint off, re-mud the wall and sand the wall again before I can attempt to paint it again.
I'm just responding because other people responded with "never seen that before", the incredibly obvious, as well as something like paint drying before it hits the wall.... NO!
It's not a one-off problem. Search the Web. A lot of people are having problems with paint that just peels off of drywall either as flaked or immediately after painting.
I'm experimenting with some fixes on pieces of drywall I have laying around but what I think will be the most effective is coat the (dried, set, sanded and clean and dry) drywall and / or mud with water glass (sodium silicate in an aqueous solution of sodium hydroxide) AKA concrete sealer at Home Depot, and then use a paint that claims to stick to glass.
Water glass does not come off of anything easily. If you find a paint that sticks to glass, floors, etc. (Home Depot has it in a separate part of the paint department) you're good to go.