Robert,
Allen addresses the possible light leak problem, and I think all ULF users have had to work around the weaksprings/weaklighttrap/mismatchedholder/nonstandardriblock problems. Your problem seems to be manufacturing error. I have no less than 10 different brands of film holders for 5 formats, and none would show such obvious generosity with film thickness. This almost could qualify as a plate holder. You bought a "film holder" and it doesn't hold your film, and it exceeds standard dimensions. I would demand satisfaction.