maybe cuz when u smoke, sumtimes some ppl have a habit of just swallowing while they still have smoke in their mouth...thats most likely why, happens to me too
once i was smoking behind a house out of a pipe took a hit out my pipe away and walked into my house started talking to my brother and all of a sudden i burped and a nice scent of bud hit the air, luckily all i had to do was let me brother get a few hits and he was cool
when i burp, it kind of burns the shit out of my nostrils because most of the time i try to hold it in but it comes out of my nose lol