Im helping a friend build there home- last month we hung the celing drywall and had a friend finish the seams (hes retired from this feld of work !) the problem is now the seams in the celing are cracking and forming a downword protrusion like the drywall is pushing out the mud and paper tape - NOT the end seams just the edge joints!!nowere else is cracking. the drywall is glued & scrwed to dry joists the roof was on before any rain hit!! what would cause this. the finisher said hes never ever seen this in 50 some years in the buiness. ANY IDEAS ???