Tested on r35615 as well as on 3.525.21. I've put a testcase on the given URL. When I fill the login form and click "Login" button and then click the browser back button, the screen isn't rendered correctly (the after login page remains, with screen corruptions added from the login form page). It's also impossible to click on anything: the after login page link doesn't work as well as login form itself. In this situation the screen is redrawn only when I tabulate three times to focus submit button. Then, also resizing browser window or changing browser font size redraws screen correctly. This problem occurs only when the password input element is filled, when it is left blank the browser back button after submitting the form will redraw the page correctly.
This bug is still present in Safari 4 Public Beta (528.16).
I'm sorry that this report has been neglected for so long. Does this still occur? The test page is no longer available.