yes they leave a "stink" oil in the butane.... just like propane, butane has no smell unless they add this... the cheaper brands use tons of this stuff, and it does NOT evaporate like butane... it stays in your oil, leaving you with that nasty ass plastic, whatever, just bad tasting in general.
I too have had my rounds with different 5x refined butane's, and really Vector is by far the best stuff to use.... Do the spray it on glass trick, if it leaves a ton of residue... you are NOT going to want to smoke it... vector leaves very very little residue when sprayed on clean glass.
Remember to cook your oil on very very low heat for an hour or so, or until it stops bubbling.
So remember if you use cheapo butane, you're gonna have cheapo hash oil, that is going to taste really bad.
VECTOR VECTOR and Only VECTOR (until something better comes along)