Problem: I have a custom checkboxes group field applied to the intermediary post type in a M2M relationship. Some of the checkboxes in this group are configured to be "checked" automatically when new posts are created, but the intermediary post created automatically by the toolset_connect_posts API does not have these checkboxes checked automatically.
Solution: Our developers are investigating this issue. Until it is addressed, an undocumented custom code workaround is required.