Flaky paint on bathroom wall - leak or damp?

[daisy12345]

Hi all, we've just had our first floor bathroom renovated a bit in Dec, took out an old shower unit that we don't need, and replastered the wall area and painted it. After last weekend's heavy snow, we noticed that the paint has become flaky in the lower part of the wall (which is a north-facing external wall). There are pipes in the wall connecting to the old shower unit, which the builders who did our bathroom have capped. Now I don't know whether the flaky paint is because those capped pipes are somehow leaking, or just damp caused by other issues. Any suggestion on how to tackle it please? I've called our builder and he'll come back and have a look tomorrow but I'd much appreciate some objective opinions too please. Thanks a lot!

Forgot to mention: We've not been using this bathroom for shower or bath at all in the last month, so it should not be caused by ventilation or condensation.

 

[daisy12345]

Update to this if anyone is interested: Our builder came back and inspected the outside of the house, didn't see any obvious cracks in the area. Also pipes are said to be capped to the floor so shouldn't be the pipes too. Most likely it was the plaster that wasn't fully dried when they painted it, so as temperature changes the paint comes off. They'll get it repainted.