Only one (first) og category is displayed for a node which is beeing submited to several groups.

Issue Summary

When you are creating a node which belongs to several groups which have og vocabularies, you check the chosen groups in the node create page, then click "Preview", but only vocabularies for the first group are displayed. Therefore, it is impossible to categorize the post in both groups.

This patch checks which groups are selected during preview instead of calling og_get_group_context function, which returns only the first group.