1. Open any existing topic, post any message.
2. Press "Edit" button on the right upper corner of the message posted.
3. Press "Preview" button
AR: Two similar "Edit" buttons are shown (one for leaving Preview mode and another for saving the edited message - please, see attachment)
ER: "Edit" button should be shown for leaving Preview mode and "Save" button should be shown for saving the edited message (now it's only done for the first post of the topic).