>Well, Utena noticed, so I expect I didn't forget. :)

to use gryphon's own words:
(I'm not eager to define it fully myself; it's a trait that the character came to me having, and I don't really feel the need to nail it down much beyond that. If I had to make a guess, though, I'd say it's a combination of several factors, psychology among them. It does get worse when she's under stress, except in the case of extreme anger, where it goes away entirely.)

I would guess that, under the circumstances of the scene in question, her anger (righteous indignation? sorry, wrong author :) overrode the stress factor.

Her stutter also goes completely away when she's sining, which is (from my understanding) incredibly common, for those whose stutter is psycological in nature