First, one thing I am 100% sure of is you did not smell propane. it is odorless.
Because it is odorless the propane people add an "odorant" to it, this is what you smell. It is there for your safety and to be honest, this is a good thing.
Normally. this "Odorant" is completly destroyed by fire when the burner ignights, and thus you do not smell it, however there are several conditions where it might survive and be noticed.
ONe: if the burner is out of adjustment and not burning hot enough
Two: If the tank is near empty, sometimes the odorant concentrates
Three: if the factory (Refinery) put too much in.
Four through many: Other reasons I do not know well enough to type about.
That said.. You do need to figure out the cause of the smell and address it.