A moisture test performed on both sides of this newly built wall is indicating a possible leak.
This could be the result of many reasons but if this is not rectified, timber rot could occur resulting in reframing sections of the wall, new wall sheeting, re-waterproofing and re-tiling.
First step to rectify is to get a plumber to perform a pressure test to identify the point of possible leak and then correct. (Then just the plaster board to be repaired and painted).
Reasonably simple and another reason to have a Building Inspection before you buy.
Servicing all of Adelaide and surrounding areas, be sure to give us call at A2Z Building Inspections when purchasing your new home.