This mud crack effect can be caused by applying a brittle paint, such as a standard matt emulsion, on top of a highly flexible product like mid sheen or silk. This problem is common when paints are applied over PVA or wallpaper paste. As a rule matt finish paints are generally brittle.
Avoid the use of PVA as a primer / sealer in all cases. Where a sheen finish or PVA is present, prime the surface with Alkali Resisting Sealer before repainting. This will also act to hold the surface together. In severe cases, where the cracks are deep, a lining paper may have to be applied.
Crown Trade Alkali Resisting Sealer