do lens changes fog IR?

[Llamapix@xxxxxxx]

I hope this is the right procedure to post a question...  Has anyone else had 
problems with fogging IR film when changing lenses?  I was shooting at Joshua 
Tree when a couple coyotes approached and I wanted a longer lens.  I changed 
my lens without using a changing bag.  All my coyote pictures are flat and 
have uneven exposure.  I can't quite tell if it's fog or not.  However, all 
the other pictures on the roll have perfect exposure.  My friend says it's 
because coyotes are tricksters.  I am looking for a more scientific 
explanation.  The camera is an old Canon AT-1.  Thanks, Gregg
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