no preview of img files if show hidden is selected

When I do a search using the gnome-search-tool for let's say .PNG files I get preview icons of the found files in the search window.
Now if I set the option "show hidden and backup files" and to the same search for .PNG files, I don't get the preview icons of the images file.

ProblemType: Bug
Architecture: i386
Date: Thu Jul 12 11:41:27 2007
DistroRelease: Ubuntu 7.04
ExecutablePath: /usr/bin/gnome-panel
Package: gnome-panel 1:2.18.1-0ubuntu3.1 [modified: usr/bin/gnome-panel usr/bin/gnome-desktop-item-edit usr/bin/panel-test-applets]
PackageArchitecture: i386
ProcCmdline: gnome-panel --sm-client-id default1
ProcCwd: /home/mike
ProcEnviron:
 LANGUAGE=en_DK:en
 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=en_DK.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-panel
Uname: Linux ubuntu 2.6.20-16-generic #2 SMP Thu Jun 7 20:19:32 UTC 2007 i686 GNU/Linux