emacs23 does not show all the buffers in the buffer menu item

Binary package hint: emacs23

Description: Ubuntu 10.10
Release: 10.10
emacs23:
  Installed: 23.1+1-4ubuntu7.1+maverick1
This is GNU Emacs 23.1.1 (i686-pc-linux-gnu, GTK+ Version 2.22.0)
 of 2010-11-26 on vernadsky, modified by Debian

I load two files into emacs, then click on the 'buffer' menu item to switch from one file to the other, but not all files are present. When I then press F10 to access the menu and chose 'buffer', then all files are present, but clicking on the first item yields the status message 'menu-bar buffer C-@' and does not switch to the file chosen. I expect that all files are listed in the buffer menu and that clicking on the buffer items switches to the chosen file.