Hi Elliot,
Not sure if this is still completely related, but even after the latest update the img field still remains broken.
Even if I create a new img field to test with. See screenshots below for the settings:
Console is empty (no js errors). Is there a way to enable some debugging info?
Same issue here, I’m running ACF 5.1.3 + WP 4.0. I’ve tested with all other plugins turned off.