watermark on album thumbnail

I've installed the watermark module and run into some problems when it comes to the thumbnail for albums. It works fine for photos.

I got it to work so that all image thumbnails and resizes show the watermark, but not the album thumbnails. For testing I tried to assign a new thumbnail to an album: in 'album-actions' for one of the items which showed the watermark, I choose 'make highlight', after which the album thumbnail was updated, but still no watermark there...

Configuration:
- versions of the image you'd like to watermark: resizes and thumbnails
- only the default watermark. only admin may change or remove
- hotlink and default enabled (added hotlink for to test, but didn't help)

I googled quite a bit, but couldn't find any information regarding the thumbnail for the album. I just guess it's supposed to show the watermark as well and I have a configuration error, but maybe this is a known problem? Or it's just not supposed to work?

When I choose one of the best photos for the album thumbnail it's kinda bad if the watermark isn't used there...

Gallery URL = http://blog.rutgers.se/gallery2/main.php
Gallery version = 2.3.1 core 1.3.0.1
API = Core 7.54, Module 3.9, Theme 2.6, Embed 1.5
PHP version = 5.2.6-1+lenny4 apache2handler
Webserver = Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny4 with Suhosin-Patch mod_ssl/2.2.9 OpenSSL/0.9.8g
Database = mysqli 5.0.51a-24+lenny2+spu1, lock.system=flock
Toolkits = ArchiveUpload, Exif, ImageMagick, SquareThumb
Acceleration = none, none
Operating system = Linux eagle 2.6.26-2-amd64 #1 SMP Tue Jan 12 22:12:20 UTC 2010 x86_64
Default theme = matrix
gettext = enabled
Locale = en_US
Browser = Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729)
Rows in GalleryAccessMap table = 19
Rows in GalleryAccessSubscriberMap table = 139
Rows in GalleryUser table = 3
Rows in GalleryItem table = 138
Rows in GalleryAlbumItem table = 8
Rows in GalleryCacheMap table = 0