PVA before plastering OK. PVA before painting NOT OK - but that's just bye-the-bye
Did you do your first coat as a "mist" coat ie well thinned (anything up to 50%) with water? If you put paint on the plaster neat the plaster sucks all the water out of the paint which subsequently cracks because it hasn't keyed in to the plaster. You should still be able to see the plaster through the first coat which is why it's called a mist coat.
2nd coat should be thinned by 10 - 25% and the final coat neat.
Which matt did you use? Supermatt is best for very new (ie barely dry)plaster. Hope it wasn't kitchen or bathroom paint - both are carp.