What possesses some software developers is beyond me. There are few things that make me more annoyed than me setting something how I want it and software then messing it up for me automatically.
So I swore at Windows Live Mail 2011 a lot. Then I found the fix. Get your registry editors out ladies and gentlemen, the key is here:
HKCU\Software\Microsoft\Windows Live Mail\Compose\Preferences\PostEditor\Autoreplace