Some flavouring or liquids with high levels of sweeteners simply gunk up a lot as the flavouring has larger molecules that bind up faster and the heat will accelerates that.
As Beamslider stated.. it basically caramelizes and the residue will gum up your coil and wick (and kill the coil's lifespan), some of it will simply condense in the chimney/drip tip.
So it's annoying, but take the tip off and a rinse with hot water with remove it easily, but do expect that your coil will start tasting off as this stuff accumulates, and you'll need to change it.