OK, so I booted a virtual 10.10.3 on VM Ware Fusion, had some folders protected, made sure they are locked (although due to later reboot this is probably not important), went to sysprefs-filevault, enabled encryption, Mac rebooted, encryption completed, I logged on new. Tried to unlock Espionage, unlock a protected folder, copy a file into it, open it, duplicate it, locked the folder, unlocked. Rebooted, unlocked, opened a file...all worked fine.
So I guess it is safe to say that it works fine. But backup is your fried, as always :-)
Thanks for your purchase, if you have further questions, or suggestions, let us know.
Zsolt