On Fri, Mar 14 2008, Reiner Steib wrote:

>   (require 'gnus-sum)
>   ;; (setq gnus-summary-line-format
>   ;;   "%«test%» %U%R%z%I%(%[%4L: %-23,23f%]%) %s\n")
>   (setq gnus-summary-line-format
> 	(concat "%«test%» " gnus-summary-line-format))
>   (setq gnus-balloon-face-0 'rs-gnus-balloon-0)
>   (defun rs-gnus-balloon-0 (window object position)
>     "Hello") ;; [1]
>
> When entering a summary buffer in Gnus, you'll see the following:
>
> ,----[ *Summary buffer* | Emacs 2008-03-14 | Current behavior ]
> | *test* O  [  22: Jason Rumney           ] Re: --script
> | *test* O  [  26: Andreas Schwab         ] Re: Emacs Bazaar repository
> `----

FWIW, Cezar Halmagean saw the same problem (see
<http://www.mixandgo.com/gnus.jpg> for a scree shot).

Cezar, do you know which version of Emacs did _not_ show the problem?
(Maybe you can try older src/emacs-23.0.60.* binaries.)