There seem to be several issues with how pigs are trading. In my last couple of games the pigs who ask for feathers refuse to accept any feathers, and the pigs who ask for manure will refuse it when offered and then start asking for petals instead.
Steps to Reproduce
Attempting to give feathers to pigs asking for feathers, attempting to give manure to pigs asking for manure.
Attempting to give feathers to pigs asking for feathers, attempting to give manure to pigs asking for manure.