Oh it's very common, leaving the bag of poo. There's lots of these stories on the 'dog pooing on my land' thread, including a few people who throw them up into trees and hedges!
As I said on the other thread, dog poo in bags is worse for the cattle farmer than just leaving the dog poo - inquisitive young cattle will try to eat pretty much anything and eventually all the rubbish they can't digest can kill them.
I think somehow we have created a society in which everyone thinks that 'someone' should make the whole world be a safe and well-organised place, and it is someone's fault if it isn't. So they think, "If no-one supplies a dog poo bin (and empties it now and again) then how can I be expected to dispose of my dog poo?"