Switching from UI15 to UI16 may show a change in the appearance of a form layout.
In UI16 there are other components installed that rely on the journal field being on a form in the same section and right before the activity stream. If the form is configured to have a field in between the journal field and the activity stream when the user switches to UI!6 the field (non journal one) will be moved to show the journal field right above the activity stream. This is the intended behavior.
This is the intended behavior. In UI16 the journal fields should be on the same section and right before the activity stream. This configuration will show the Post button.