Well, I seem to be having a rather odd problem. I've set up my installation to create a couple of thumbnails: the standard 'thumbnail' 'medium' 'large', as well as one custom size i created with add_image_size 'homepageleadthumb'.
When I upload an image... it works GREAT! When i use the the_post_thumbnail( '....' ), it works flawlessly, for all of them.
The problem occurs when I choose to crop the thumbnail image in the 'Edit Media' screen. When i do that, all the size options no longer work with the_post_thumbnail( '....' ) function, except for in the case of the_post_thumbnail( 'thumbnail' ).
Meaning... the 'medium' 'large' 'homepageleadthumb' thumbs are useless. In those cases i just get served with the full-sized original image. However, the the_post_thumbnail( 'thumbnail') does serve the correct (now cropped) image.
Further, as long as i dont crop the image, i can upload an image, it can create all the image sizes, and i can deleate all of them from my server if i choose to.
However when I crop said image, after uploading, it does create all the image sizes in my server, but if i choose to delete it, it only deletes the original image and the 'thumbnails', the 'medium' 'large' 'homepageleadthumb' thumbs are left on the server.
Esentially, it seems that wordpress "forgets" that it even created those "other" sizes, once i crop the image...
I'm running WordPress 3.5, and this wasn't a problem untill after i updated to 3.5.