PROBLEM No cache for thumbnails

[Hypertexter]

Hi,

on my site I added some entries to .htacess for caching image files like .jpg and .png:

Code:

...
ExpiresByType image/jpeg "access plus 2678400 seconds"
 ExpiresByType image/png "access plus 2678400 seconds"

and

Code:

# Cache specified files for 31 days
 <filesmatch "\.(ico|flv|jpg|jpeg|png|gif|css|swf)$">
 Header set Cache-Control "max-age=2678400, public"

Google Pagespeed recommended it - and likes it now.

But now I saw that the automatically generated thumbnails of Getsimple, which are jpg files, are not cached. They are small, but I would like to know why they are not cached? I see it in Firefox, when it says "Size unknown - not cached".

Thank you
Hypertexter