[Plugin: Regenerate Thumbnails] only shows medium thumbnail

hi,
i have following problem using this plugin: it only shows after regeneration the medium thumbnail and resizes it.

i did:

1. istallation ok
2. media settings -> from 150×150 to 100×100
3. regenerate image ok
4. edit post: featured image shows 100×100
5. index shows: 300×120 scaled to 100×100
6. template index.php: the_post_thumbnail(array(100,100), array('class' => 'alignleft'));

so – what went wrong?

thank you
NIC