I found out that when pressing back button it gets previous page from browser cache even if I send following headers:
Test1.aspx
Server
expires should be a date+timestamp and cache-control"s "must-revalidata" & "max-age" might help as well?
Expires: Wed, 11 Jan 1984 05:00:00 GMT Cache-Control: no-cache, must-revalidate, max-age=0