sess_write Does Not Save Updated Information if Global $user is Changed

If the global $user is changed in execution (e.g. devel_switch_user), sess_write does not seem to save that information. Upon page refresh, the original $user object is loaded into global $user.

This appears to be an issue with the $is_changed variable in sess_write - it should check to see if the global $user->uid has changed since the $last_read.

Is anyone else experiencing this issue? Attached is a patch for a possible fix that seems to work on my setup.