Seems to be fixed by JC-813.

1.Login and click on 'Message(N)' link
2.Enter some text to message and/or title field(s)
3.Press 'Back' button
Actual result: You are redirected to previous page. No warning message
Expected result:'Alert'- window appears with message 'Do you want to leave this page without saving?' and 'Yes','No' buttons

Still reproduced in PM, topic and posts on uat and deploy instances

Browser cache clenup may be necessary

Create new topic
Fill any fields: "Topic title", "Message content", "Poll", "Option list". Click "Back" button.
Actual result: You are redirected to previous page. No warning message
Expected result:'Alert'- window appears with message 'Do you want to leave this page without saving?' and 'Yes','No' buttons

Checked on deploy.jtalks.org, all these field behave as expected at least in chrome.

1. Have you cleared browser's cache before trying?
2. On which instance have you tested it? mb fix was not delivered there yet?
3. What browser you're using?

Zaur Sejfulaev, please answer the questions above and close the issue if it is OK now.

Checked in Chrome and Firefox, in uat.jtalks.org/ After the cleared browser's cache, all works.