This AP article seems to catch the heart of the dispute:
According to the mandate, the investigation should focus on Palestinian victims of the three-week war between Israel and Hamas earlier this year.
But Goldstone, a Jewish former judge of the South African constitutional court, said his team would investigate "all violations of international humanitarian law" before, during and after the conflict that ended Jan. 18.
"It's in the interest of the victims. It brings acknowledgment of what happened to them. It can assist the healing process," he told reporters in Geneva. "I would hope it's in the interests of all the political actors, too."
Martin Uhomoibhi, the council president, explained the apparent contradiction by saying the mission always intended to evaluate the proportionality of Israel's response, which requires that acts of both warring parties be examined.
It will be interesting to see a) how vigorously Goldstone pursues his claimed mandate over violations committed by both sides and b) how the UN bodies will react if Goldstone does do more the engage in a pro forma critique of Palestinian human rights violations.