[FancyCyclops]

Read title.
To elaborate, shades can fade without the user being revealed if the enemy misses the user. This makes the user untargetable, and as a result can lead to some... strange things.

Like being semi-invulnerable. I don't have much to show, BUT

[Neus]

Needs more details on how specifically to reproduce it.

[Fern]

If you use Create Shade as a Spellthief and someone guesses your position correctly, but misses you with a basic attack (or when you proc Cobra's Snake Dancer) the Shade will take damage, but you will remain invisible.

I presume this is because the game waits for your character to take damage before making your icon visible, but since the shade is the one that gets hurt, you remain invisible until your next turn.