Stylus can't remove all styles. There's simply no such code. Nothing related to style management was added recently.

AFAIK there's nothing in Stylus that could possibly trigger this kind of bug in FF Nightly. I've seen many nonsensical bugs in FF Nightly over the last year so that must be just another one.

The problem seems specific to this build of FF Nightly, see http://forums.mozillazine.org/viewtopic.php?f=23&t=3040021