zsh doesn't understand some multibyte characters

[Danek Duvall <duvall@xxxxxxxxxxxxxx>]

Perhaps this is just on Solaris, I dunno.  But for some multibyte
characters ("…", for instance), if I type them on the commandline -- either
using the Compose key on my keyboard, or via insert-unicode-character or
insert-composed-character -- then if I move the cursor back over them or
delete back over them, zsh gets confused and moves two positions instead of
one:

    $ PS1='$ '
    $ …_ (cursor at _; now hit backspace once)
    $_

I do have access to a Linux box running 4.3.17, and it doesn't seem to be a
problem there, but I don't know whether that's because of a different
version or a different OS.

I'll note that the same thing happens with all the other shells on Solaris,
so I'm guessing it's not directly a problem with zsh.  FWIW, bash (and
libreadline) is compiled with Solaris curses, while zsh is compiled with
ncurses, so I'm guessing it's not that.  But vim has no problems
whatsoever (old Solaris vi does).  Where else should I be looking for the
problem?

Thanks,
Danek