~cyb/image/maps is a directory containings many JPEG world maps and
~cyb/maps is a symlink to it:

drwx------  3 cyb cyb 4096 2005-01-31 10:39 ~cyb/image/maps
lrwxrwxrwx  1 cyb cyb   10 2004-10-12 21:04 ~cyb/maps -> image/maps

When I open the directory with Nautilus, the thumbnails are displayed
instantly thanks to the cache but when I open the symlink instead,
Nautilus builds another version of the cache for the same files.

It takes a while to build it and I guess it also wastes diskspace
under the ~/.thumbnails/ directory.

Nautilus should recognize that ~cyb/maps and ~cyb/image/maps are the
same thing.

Thanks.