set_post_thumbnail_size works not the way it should

The function < ?php set_post_thumbnail_size( $width, $height, $crop ); ? > doesn’t work as I expect it to.
I want thumbnails with 200px width and 130px height and always these sizes. Always. But not with screwing the dimensions. That means: Crop. So that was what I used in functions.php:

<?php set_post_thumbnail_size( 200, 130, true); ?>

Right?
But what it does (which is the exact thing what it does when I use “false” is, that it keeps the dimensions. Uachh! It displays some sort of 200px wide image but with different height or something else. It *should* CUT the image so it doesn’t look f*cked up but still has the intended size for *every* thumbnail on the index. Can that be so hard?
Apparently.

Can somebody help me out here?

Thanks! Appreciate it!