FormsAuthentication Cookie Caching

FormsAuthentication Cookie Caching

I am having an issue where my authcookie is not being dropped on browser
close, or when a different user signs in.
My cookie is declared here:
If ModelState.IsValid Then
'check username and password
If model.pwd = db.users.First(Function(t) t.NT_id =
model.NT_id).pwd Then
'create an authentication cookie
FormsAuthentication.SetAuthCookie(model.NT_id, False)
'set to false to destroy cookie on browser close
'redirect action if login is successful
Return RedirectToAction("Construction", "Home")
Else
ModelState.AddModelError("", "Invalid Username or
Password")
End If
End If
Return View(model)
I know this isn't dropping the cookie because I have a variable to show me
the cookie username
Public Shared uNT_id =
If(HttpContext.Current.User.Identity.IsAuthenticated,
HttpContext.Current.User.Identity.Name, System.Environment.UserName)