We can revert by using the CTM (Cygwin Time Machine):
http://www.fruitbat.org/Cygwin/index.html#cygwintimemachine
I'm hoping to do that this weekend on my XP machine and see if I can pin
down when the problem started. I made some incorrect statements about
that earlier in the thread.
The problem was first reported on the list on May 11:
http://cygwin.com/ml/cygwin-xfree/2012-05/msg00007.html ,
and the poster said he had updated on May 10. This is the day it was
announced that the GNOME libraries were updated to 3.4.1 and that cygwin
was updated to 1.7.15.
The CTM has a snapshot dated 2012-05-08, which is probably a good place
to start.