Hm, weirder still: I can confirm what @frostschutz just said: FW 5.9.x doesn't do any FBIO* ioctls when switching to/from the Homescreen on the H2O.
Which would imply that if ioctl race there was, it'd have been between concurrent instances of fbink itself, which would: one, take some effort to actually achieve (and, err, I would just say try to avoid doing it?
); and two, makes this even more mysterious as it never ever does a FBIOPUT... :?
Gremlins? ;p