Information leaks with automatic searching via URL bar.
In the Tor browser, if you enter a malformed URL, it immediately thinks it's a search query and pushes that malformed URL over to the assigned default search (DDG, Startpage, etc)
This is a type of information leak.
It would be better if a malformed URL is entered and you press Enter, you're asked if you are sure you want to search for this or not.
It could be in a strip appears under the URL bar, like the strip that appears when you first run the Tor browser for the first time asking about the default configuration, or a popup from the URL bar, like the enable canvas or enable notification popups.