I emailed Purolator concerning this issue, and they wanted to see the filter. They sent me a pre-paid next-day air shipping kit. When they received it, they disassembled it and determined the incorrect end cap was installed, one without a relief valve. I was assured this was a fluke, that their quality control is usually better than this, and all stock will be inspected.
For my efforts, I received a complimentary case of filters.