This happened to me twice under the same circomstances:
When the edited file is modified by an external
program, NEdit detects it and asks for reload/dismiss.
If the file is stored on a NFS volume, the information
about the file change may arrive with a considerable
delay. If this information comes at the moment when I
already manually picked the "Revert to saved" entry
from the File menu and the dialog box is waiting for my
confirmation, the NEdit crashes so badly that it hangs
the X-windows (In my case the
keyboard seemed to work somehow, but the mouse was
gone). I could not restore X-windows from network, and
I had to kill X to recover.
I am using NEdit version 5.1.1, RedHat 7.1 Linux (same
behavior on RedHat 7.0).