I can't get the og_group_ref set in a node form rendered via a custom block
For the benefit of others, I realized the user was not a member of the child group they were trying to add content to. They were members of the parent, but that didn't allow them to add content to the child group in question, so permissions didn't propagate as expected. There is an OG subgroups module (https://drupal.org/project/og_subgroups) which is supposed to help with this, but I wasn't able to configure it correctly for some reason before realizing that this particular application required the user to be a member of the subgroup in order for them to actually post.