clone-buffer creates strange error msg: Cannot clone a file-visiting buffer

[leo]

hi there

in info sitting in the top node i can execute clone-buffer and it works just
fine. when i go into the emacs manual or the elisp man and i execute
clone-buffer everything's fine, too.

but then: i go into the info-file of info it self (title: "Info: An
Introduction"), execute clone-buffer  and now i get the strange error
message: "Cannot clone a file-visiting buffer". why? i'm still inside info
(info-mode is switched on).

any clue?

leo