Its funny how little things like that can actually spoil a hunt. I remember years ago when I was in the Army they taught us that even using the wrong soap was enough to signal your presence. I remember smelling cigarette smoke from a guy smoking about 500m away...it would have gone further if the wind was up. Flatulence is one of those aromas that is peculiar to a species, and let's face it...human flatulence can be pretty potent...potent enough to signal the fact that we are there....how many times have you walked into a cloud of gas and there is no-one nearby that you can blame it on...it can certainly linger.
As for the wind blowing...it's surprising how many animals go into cover when its blowing...it plays havoc with their olfactory senses.