I run into this issue for a long time, so I surprised I could not find bug report about it (or maybe I'm bad at searching).
Go to some repo, go to Source page, browse into some directory. Try to go back from it using browser back button. Url changes, but the page stays the same. Issue may disappear if I manually click on parent directory, but it gets back again if I reload the page (F5). Tried in Google Chrome and Mozilla Firefox.