I can echo.
My testing on this found:
FRESH install of 4.5.1
6 expected combinations of the following
without and with AD fix from http://dnn.gmss.org/DNNModules/tabid/312/Default.aspx
without and with My fix for autologin http://www.dotnetnuke.com/Community/ForumsDotNetNuke/tabid/795/forumid/89/threadid/55339/scope/posts/Default.aspx
without and with impersonate=true username etc.
without and with detailed domain info in auth settings
without and with role sync
clear of cache and restart of application after all changes

In child portals/all combinations:
Autologin functions once for one child portal but if user changes pages or browser is closed and session ends, user is forced to login manually.  If user closes one child portal that autologged in, no other child portals will autologin for quite some time.    What’s more puzzling is we created a test network account via our template that emulates most other accounts tested.  This account does not log off after page changes and will re-autologin if site is reopened or another child portal is opened.  I tested this failure across no less than twenty user accounts.  Only one account seemed immune.
Root portal will not log out user on page change.  Navigation from root portal to child portal will prevent autologin to child portal and subsequent attempts to autologin root or child portals. 
Also: manual login will throw "Object not set to instance of object" error for some users after logout.  I have yet to see pattern.
For those users that can manually login, authentication is stable and will not logout from page to page.  Manual login will not help autologin to other child portals in other browsers.

Obviously this is not good. 

DNN 3.3.5 with AD Fixes from resources as listed above, allows users to close a child portal browser and subsequently open and autologin multiple child portals in multiple browser windows.  Only manual logout will emulate above behavior.  All accounts perform the same.

The successful instance of 3.3.5 and the failing instance of 4.5.1 are on the same network and tested with the same accounts.