I think it's mostly the number of common homophones and the speed at which most English speakers think and type that causes the problem. Add that to obscure language rules and you can end up with something that looks completely wrong, but isn't.

A great example is "red-head scarf"; what you read is "(read head) scarf" what it means is "red (head scarf)". Granted, it makes the wording unnecessarily complicated, but it's probably grammatically correct.