Haven't seen it.
I have yet to see it actually do any damage at all.
I've been traveling extensively (recently) with flim in my carry-on and I haven't seen any degradation whatsoever. From ISO 100 to 3200, nothing.
I'm sure it's possible, but I'd bet it would have more to do with temp. change than anything else.
In the past I've just asked to hand it over to the checker and have them inspect the canisters by hand. Not always easy, i had to be very persistent.