I have a FDE enabled on my Android. However on JellyBean when device restarts I never get a boot password prompt,just regular unlock screen. I remember on 4.0 ICS, after reboot Android would ask me for decryption key so it can mount the /data filesystem. My device is Moto Droid 4. I verified from command line that /data mounted with encryption, however I cant figure out where it gets the key from,if I never have to enter it on boot.
Are you sure that you have enabled FDE? I've read this link which states that FDE may not work directly as expected (must try in 4.2.2 multiple times), and that you need a PIN or Password defined in advance. I mean, if you can access your data without entering a security credential then your device is probably not encrypted right? Watch out FDE may not encrypt all the things you think it should: Does Android's Full Filesystem Encryption also Encrypt the SDcard?