Change "Edit" button to "Save" button for all Edited posts

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).