Bootcamp and Filevault 2 boot to OS X before a restart allows Windows to load
I think it's a timing issue, you need to ensure that you press the option key early enough in the boot process to stop the normal boot and subsequent Fielvault login.  The best way to do this is to ensure you have not muted the machine to you get the "bong" noise when you start/restart your machine.  You need to hit alt/option immediately when you hear this, and keep it pressed for 5 seconds or so.