In the skill description states that Spread Your Wings grants a "floating" buff, which lets you ignore surfaces. This, however, only works while moving. In the moment the movement stops, you get the contact event and slow/burn/etc debuffs kick in normally.
The character animation might hint this behaviour as intentional, as the character actually touches the ground while standing still, and does not while moving. However, other (permanently-)winged characters (tested on enemies only) which share the same animation and buff are unaffected by surfaces all the time, and not only while moving.
If this is not a bug, which I personally think it is, it should at least be clearly stated on the skill description.
I've also noticed that surfaces with certain "height", such as cursed fire, also affect winged characters, regardless they're moving or not. I'm not sure if this is intentional, but I thought it is worth noting just in case.
As a personal opinion: In the current state, Spread Your Wings is a mostly useless skill on combat. There are better ways to make big leaps, and it does not help with positioning either. Cost is low, yes, but it last very few turns and it requires two points on Polymorph, so it doesn't fall into the almost-free-so-good-to-have category. If the stated behaviours are intended, please consider giving it a little buff.
EDIT: Forgot to mention this happens on GOG's 3.0.171.819.
Regards,
R.
Last edited by Roobre; 19/02/18 03:44 PM. Reason: Clarify that enemies also have the same "Floating" buff