Thanks to all who replied, especially the snark.
I'm replying this way because mailings from the list have been disabled. Excessive bounces, they say.
the system in question is a laptop, so there's only one kbd, and its not USB.
The problem is that for no apparent reason typing on the kbd does not produce and input to, say, gnome-terminal. This happens with any app that accepts kbd input. It does not apply to the mouse.
Logout-login (via GDM) cures the problem, until the next time, so the kbd is not broken.
Pointers to bugzilla and fedora forum are much appreciated. I'll try the workarounds suggested.