Hi @summerz
The issue looks to be the acf_form_head is the function which generates the javascript variables acf.o.post_id
It seems that because you are customizing the post object, this is most likely not being set correctly by the acf_form_head function.
Can you take a look at the source / firebug and make sure the acf javascript variable exists and contains the acf.o.post_if value?
