Recently working with wordpress 3.5, I came across this patch :http://core.trac.wordpress.org/ticket/19889
…which solved the problem of custom image sizes defined by my theme not resizing or rotating properly. The issue was image-edit.php did not account for sizes added by the function add_image_size (i think this is the name of the function but not 100% sure) in functions.php.
this patch worked perfectly but unfortunately it does not work on 3.6. image-edit.php seems to have been replaced completely by different files and functions.
I could backup to 3.5 but the best thing to do is fix it under 3.6! I am not an experienced coder so I wanted to ask someone to have a look at the patch and help me go about fixing the .php file now responsible for editing images.
