Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 12986)
+++ wp-includes/media.php	(working copy)
@@ -64,8 +64,6 @@
 	} elseif ( isset( $_wp_additional_image_sizes ) && count( $_wp_additional_image_sizes ) && in_array( $size, array_keys( $_wp_additional_image_sizes ) ) ) {
 		$max_width = intval( $_wp_additional_image_sizes[$size]['width'] );
 		$max_height = intval( $_wp_additional_image_sizes[$size]['height'] );
-		if ( intval($content_width) > 0 )
-			$max_width = min( intval($content_width), $max_width );
 	}
 	// $size == 'full' has no constraint
 	else {