Loading cycle and Session variables

I am setting a session variable when the user selects a value from a dropdownlist (SelectedIndexChanged) in webusercontrol #1.
The page then refreshes and I thought that webusercontrol #2 on the page should be able to access the session variable in its page load.
However the session variable is not available until the user refreshes the page again. I'm assuming that the page is refreshed before the session variable is updated.
 
How do I fix this ?
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