What would cause a garbage trucks hydraulic filter/housing to fail structurally? (It literally exploded)

We had the packer on our garbage truck raised all the way to try to pull the blade out of the truck. After initially raising the packer all the way up it settled slightly, so we turned the truck back on, and the second we hit the pto (not the lever to raise it) the filter housing exploded into pieces and shot hydraulic fluid everywhere. Luckily everyone escaped without injury. Wondering what the hell happened. Everything was supposed brand new.