I just installed Sidekick and uploaded an image that was originally 2560×1920 pixels big. I attached it as a featured image to my post, then realized it was too big and went into WP's media manager, where I resized it to 2560×403 (thus being wider than 1500px and shorter than 500px, as required by the code:
if ( $image && $image >= 1500 && $image <= 500 ). However, the function call to
wp_get_attachment_image_src( get_post_thumbnail_id(), 'sidekick-panoramic' ) still returns
Array (  => http://.../wp-content/uploads/2013/06/WP_002681-666x500.jpg  => 666  => 500  => 1 ); the URL being for a thumbnail created of the original - not the resized - picture.
I seem to be not the only person with featured image related problems: http://en.forums.wordpress.com/topic/sidekick-theme-has-no-panoramic-header-option-as-shown
I'm sure it's an oversight on my part, and I'd appreciate any and all pointers you can give me.
P.S.: I'm not sure how the following quote from http://theme.wordpress.com/themes/sidekick/ goes together with the actual source code above:
Sidekick will display a post’s featured image, full browser width, if its aspect ratio is at least 3×1 (width x height) and its minimum width is 1500px.
If the picture is 1800×600px, the text says it'll work, the source code says (if I understand correctly) it won't.