nul character ^@ (set-mark-command) binding ignored

[Rodger Anderson <rodger@xxxxxxxxxxxxxxxxxxx>]

I'm having problems with the nul character, ^@, which is normally
bound to set-mark-command.  It appears that the nul character is being
ignored.

I've verified that I *can* send the nul character via cat -v.  With my
current keyboard in an xterm, I can use shift-control-2 (control-@) or
control-spacebar.

I've verified that the set-mark-command works by setting it to another
character via the bindkey command: bindkey "^Z" set-mark-command.

I can bind ^@ to other commands, but they don't get executed either
when I press control-spacebar.

This is with version 2.5.03.  My OS is HP-UX 9.05 on 9000/715.

Version 2.3.1 works as expected.

This seems like a rather strange problem, as I've not seen any mention
of it on zsh-users mailing list before.  Doesn't anyone else have this
problem?

Rodger Anderson