Thailand has accepted that the temple belongs to Cambodia. ICJ ruled that the immediate area around the temple was Cambodian territory in 2012, which is a 0,35 square kilometer area mentioned in Cambodia's initial filing in the 60's. Cambodia have since tried to lay claim to a larger area of 4,5 square kilometers, which Thailand opposes.
"So in fact who is making the problems"
Cambodia is, by digging trenches, fortifying both existing and new positions in the area, and, seemingly, laying mines in the area since March, in violation of the MOU (and this is just a few instances of the MOU violations they've perpetrated in the area). They then decided it was a good idea to open artillery fire on civilians, including children.