Attachment_fu stores the wrong size

hello,

I am testing attachment_fu to load and store images.
I am resizing them and generating a thumbnail but apparently it saves
the wrong size in the DB :
- the image has the original size
- the thumbnail has the size of the resized size

I am using Rmagick 2.5.2, Rails 2.0.2 on a Mac with X.5

Thanks for your help
Nicolas