My 545 has the same problem as Kip's. I've stripped it down and muddled around with it, but never found a fix. I take the holder off the camera and 'help' the packet out by pushing gently on the film part while pulling the tab.

'Lock and lock' make some nice kitchen containers that are completely watertight - they have an elastomer seal and locking tabs. They're great for carrying around Type-55 negs in the field. See here: www.organize-everything.com/loandlostco8.html.