All the fillers should have contact with the bridge or you'll get a horrid burning taste which means no juices are reaching it - a too dry bridge will burn the filaments inside and will ruin it (the only way then to fix it is to remove all the filaments which makes the atty pretty much useless unless you drip exclusively). WHen the bridge makes contact it makes itself a little nest in the top of the filler and the vaporisation of juice can discolor the filler material, but it shouldnt singe or burn. The discoloration usually comes from the coloring in the juice, not being burnt by the bridge (Ive not seen this happen with plain PG - you get the indentation mark but no discoloring).
You *can* however melt the end of the carts if your atty gets super hot (mine get very hot, and Ive melted a few cart ends and I drip I dont use any filler) - but you dont inhale anything, it just shrinks back on itself. I slice a tiny piece off the bottom (cart end obviously, not mouthpiece lol) and it wont happen again.
Its good you asked, Im sure there's at leat one other person out there who was wondering lol.