If you can do that same cone, with a different liquid, then I'd say it was bad juice.

Haven't heard of that, but I imagine it could happen. So far I've been fortunate. There's nothing in the cone to create a burnt flavor. But, perhaps it's a lingering thing. I soak my cones as well as my attys, so, if it continues with more juices, I'd soak the cone as well. The vinegar is incredible for breaking that nasty stuff down (mind you, I've never had it revive burnt silicone.

)
I've also had a cartomizer with bad silicone wicks that never wicked and always tasted burnt. But so far with my eroll I haven't ever had 'burnt' stick around. Even with running them out of juice and everything.

(Then again, I'm a recent convert to the eroll, who just has read a lot.)