It's not wind that gets inside the holders and causes film to pop - it's usually a combination of humidity change and temperature which can cause the film to "pop" into a slightly different position. Also, you may be looking at film simply dropping down slightly in the film channels within the holder to due gravity - at some point during the exposure, it may be slipping down. A good tap or two along the top of the holder once it's inserted almost always guarantees that this won't happen and it helps if you have holders with tightish rails. The "popping" problem is a little more difficult and you should probably do a test with a holder where you have stuck a small piece of double sided tape on the middle of the septum holder and then tap the film onto it when you're loading it...
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