I was able to fix this by changing api/api_field.php
on line 789 from:
$data = maybe_serialize( $data );
Once single slashes are replaced with double slashes (which then get escaped back to a single slash in the database post_content) it saves the proper serialized data and can be loaded correctly.
$data = maybe_serialize( $data );
$data = str_replace('\\', '\\\\', $data);