Can't set Fancybox image as a format in manage display of a content type, or hide a field.

As the title says - when i try to set a format in manage display of a content type to a Fancybox image - Drupal just doesn't save it. The clock icon appears near the format listbox, and does nothing for eternity.

Same thing when i'm trying to hide a field.

Also - when I deleted 13 April release and installed an older version, everything returned to normal. So these bugs are from new release.