Apparently the problem reported by Stephen in
http://www.xemacs.org/list-archives/xemacs-beta/200010/msg00190.html
still exists in 21.2.37, although I had to set
`buffers-tab-filter-functions' to nil in order to see the tabs of all
open buffers. Previously, I just had to set
buffers-tab-max-buffer-line-length 25
buffers-tab-max-size 6
to get all of the tabs.
Markus