Have you poured enough water when they were plastering? It also happens due to less amount of water supply as plaster soak lot of moisture. Do they plaster in summers as these cracks may also be due heavy sunlight.
In my opinion do not go for prices. Try best paints so that it remains for a longer time. Money once invested should pay back for at least as much time as possible. Try to search for good painters too.
Dry the plaster previous to apply paints otherwise patch will be formed. Heaters could not have a healthier result. It could only dry on the outside surface but not in the interior. Moisture will remain in walls resulting terrible impressions.
I am with you; these flashes could be due improper applied emulsion. Previously, patches of emulsion were not prominent and hence resulted in color patch. Now just rub patch area and then again follow the process.
I have by no means faced such quandary but in my opinion, eradicate base coat using sand paper and then make an effort to fuse wall paper. May be your dilemma get cracked.
I have the same opinion to Dec, use fine quality of paints. I will go with Dulux paints. I make use of it and have complete confidence regarding permanence.
Firm counsel! I am Abner Wright, newbie. I think 2 coats are sufficient for accurate color and permanence. If using wood primer also then 1 coat can also accomplish needs.