Sharepoint problem: switching user correctly but internaly maintains "old" user

I'm facing an extrange behavior in my Sharepoint 2077 farm: We have configured windows integrated authentication with NTLM, and all clients authenticates correctly to the portal. When they proceeds to "login as" diferent user, it seems to be all fine (appears user name in top of page) , but internally the page user is the old user. I know this because I have a customized web page that reads page user name and print it to the page. after some refresh or waiting some time, the current user is applied "internally" too.

Do you know is there is any configuration option for avoid this开发者_StackOverflow delay?

Many thanks in advance, any help would be appreciated.

solved there: http://support.microsoft.com/default.aspx/kb/970814