I don't recall ever failing an illusion after mastering, but I managed to do just that a minute ago. Is this a bug or just something that happens so rarely I've not noticed?

>il voi
You hold up your hand, palm facing up, and concentrate on creating the illusion of a void. Inky black lines appear in the air hovering over your hand, and you feel a distinct pull of air towards this point. A faint ripping sound echoes out from your palm as a black void slowly opens. Before the void becomes whole, an errant black tendril causes the entire illusion to unravel before your very eyes.
Roundtime: 1 sec.


You are a member of the Sorcerer Guild.
You are current with your dues and must check in again sometime in the next 34 days.
You currently have 75 ranks out of a possible 372 for your training.

You are a Master of Illusions.

That's possible; didn't think about that.