Thumbnails width block

Hello,

I don’t know why, my thumbnails are blocked at 163 pixels, even I set values like that:

add_image_size( 'thumb-small', 350, 250, true );
		add_image_size( 'thumb-standard', 420, 300, true  );
		add_image_size( 'thumb-medium', 420, 300, true );
		add_image_size( 'thumb-large', 450, 320, true );

I am using single list blog.
I also use regenerate thumbnail plugin after i modified values.
And something strange is I can change the heigh without problem.
Just the width doesn’t want to go more than 163px (of course my image is bigger than 163 px).

Anyone have a clue for me ?

Thank you !