Dealing with this issue, trying to post OG Content to Drupal using Services: https://drupal.stackexchange.com/questions/159149/setting-og-with-services-module

patch--og_form_group_reference_validate.patch

diff --git a/og.module b/og.module
index 6f28205..a3aa3be 100755
--- a/og.module
+++ b/og.module
@@ -762,6 +762,12 @@ function og_form_group_reference_validate($form, &$form_state) {
     if (!empty($form_state['values'][$field_name][LANGUAGE_NONE])) {
       return;
     }
+
+    // @TODO: Find out why the 'og_group_ref' field isn't getting maintained in the 'values' array by form_builder()
+    if (!empty($form_state['input'][$field_name][LANGUAGE_NONE])) {
+      $form_state['values'][$field_name] = $form_state['input'][$field_name];
+      return;
+    }
   }

   // No group selected, throw an error.