How bad is the bend?  Acetate can take some 
abuse, short of an actual creasing (unlike pencil 
boards, of which I've gotten some mangled).  

All I know is once you give up the package, you 
probably won't ever see it again. 

I was once told that with UPS you have to refuse 
a package as it's being delivered to make a 
claim. With the USPS, I'm not sure that is the 
case, but I do hear the whole "insurance claim" 
thing is a rough procedure to go through and I 
think you'd have to prove somehow that the damage 
occurred while the USPS had their hands on it. 

(In a semi-related topic, don't think that just 
because you go through the procedure to determine 
that a money order has disappeared into the 
ether, that you'll never end up screwed.  I had a 
missing MO addressed to another address on Long 
Island, be cashed somewhere upstate NY (with a 
block-letter signature!), 7 months AFTER being 
declared missing and refunded, and I'm now 
responsible for "returning" the refund!  When I 
complained that it should be in the US PO 
computer system as declared missing, they 
said, "We can't refuse to cash a money order!")