Browser message page is shown instead of forum page when user clicks "Back"

When user starts a topic or create private message and fills some fields incorrectly, then clicks "Back" from the page, he sees "Подтвердите повторную отправку формы" browser message

Pre-condition

1. User is logged in
2. Topic creation form is opened

Steps to reproduce

1. Click "Send"
2. Fill all fields correctly
3. Click "Send"
4. Click "Back" (in browser)

Actual result: "Подтвердите повторную отправку формы" browser message is shown

Expected result: user is redirected to the topic creating forum page.