I run 2.5.1 on my blog and previously I use thumbnail named as myimage.thumbnail.jpg, since I upgrade to 2.5 I use myimage-125x125.jpg. I order to use the right thumb I upload to my upload folder new thumbs with the new name structure.
I change also data in the wp-postmetadata table with this sql command :
UPDATE wp_blog4autopostmeta SET meta_value = replace(meta_value, '.thumbnail','-125x125')
But when I do that I have a error on the media library :
Warning: Invalid argument supplied for foreach() in /home/www/myfolder/wp-includes/media.php on line 264
Thanks for your help