Google Chrome in Incognito Mode still logging visits history
It would appear you are running into the intended feature of the omnibox, it will give you auto-suggestions pulled from the internet as you type.
If you start typing 'superu' it may bring up superuser.com even if you have never been here before. this is not instant search as you mention you do not have enabled, instant search is an extension of this where it will actually load the best result, aka your feeling lucky, as you type. with instant search enabled it would already be loading superuser.com if you started typing it and it was the best result based on google magic.
Turning off Auto-Suggestions
Clear your browsing history
Click the Tools menu
Select Options
Click the Under the Hood tab and find the ''Privacy section
Deselect the 'Use a suggestion service to help complete searches and URLs typed in the address bar' checkbox.
Click Close.
referance: http://productforums.google.com/forum/#!msg/chrome/0DR-pLIVI5g/XuqF5qasts8J
The Incognito window in Google Chrome is meant to allow you to browse without storing your history or cookies that will connect your browser to your searches. If your primary problem is the auto-completion/auto-filling of addresses, just clear your history.