Hi John
I didn’t wait for an updated version of ACF to solve this issue (I posted the support request nearly 2 months ago).
Instead I used a workaround in the form of some ACF form overrides, a custom AJAX callback, some ACF actions and some WordPress AJAX actions. This sends its own modified AJAX request to ACF, and some hooks perform some overrides to return JSON objects (for validation and saving respectively) rather than just redirecting. Then I was able to capture that data to do whatever I wanted (in this case displaying a success message rather than redirecting).
See the following code sample: http://pastebin.com/L55bNyu7
Cheers
