windows xp - Switch Ctrl and Alt with AutoHotKey without messing up the Alt-Tab switcher?

I want to switch the Ctrl and Alt keys in Windows XP. I created an AutoHotKey script that contains the following:

LAlt::LCtrl
RAlt::RCtrl
LCtrl::LAlt
RCtrl::RAlt

This works, but the only problem is that the Alt-Tab switcher gets stuck. When I release Alt-Tab, the window switcher stays up until I hit another key or click the mouse.

Does anyone know how to fix this problem?