delete \thumbnails dir to regen thumbnails broken in v12

I am in Win8. Prior to v12 Frodo, I was able to regenerate thumbnails by deleting C:\Users\<user>\AppData\Roaming\XBMC\userdata\Thumbnails. However this is broken in v12.

I don't know any other method to generate. Actually this has been a pain already, when I update the thumbnail for 1 movie, deleting the dir regen all 500 movies thumbs...