Thumbnail size/cropping won't change

I looked on these forums and couldn’t find anyone with my exact same situation. I’m trying to get my post thumbnails to be uncropped and 300x225px. In my functions.php, I have this:

if ( function_exists( 'add_theme_support' ) ) {
	add_theme_support( 'post-thumbnails', array( 'post' ) );
	set_post_thumbnail_size( 300, 225, false );
}

When I changed this from true to false, I thought this would stop the thumbnails from being cropped, but it didn’t do anything. What I don’t understand is that some of my post thumbnails are working just as I would expect–they have a width of 300px and aren’t cropped–but my newest posts thumbnails are 200x200px cropped. Here’s what I mean: http://www.iymeko.com/blog/

I tried removing the featured images from the problem posts and putting them back in, which did nothing.

Any and all help is appreciated!