There appears to be literally a zero percent chance of thief traps failing, or the victims of said traps saving against them. I have a feeling that this is a bug, since this cannot possibly be designed to have no chance of failure or save like virtually every other blindness or spell-like effect in the game.

If it is not a bug, perhaps put it on the roadmap of things to consider. A 100% effective blindness (or immolation, or boneshatter, or or or) is, for obvious reasons, pretty ridiculous an eliminates all risk for these characters.