FileVault 2 bootup login gets weird after crash

I have had FileVault 2 encryption enabled on my laptop for almost a year. It's worked well and I've never had trouble... until yesterday.

My computer froze while I was saving something in Photoshop and had various other apps open. Nothing unusual. This happens once in awhile so I wasn't troubled by it. I have a TechTool Pro (TTP) emergency boot partition installed, so I booted off of that and ran Disk Utility and TTP to check the encrypted disk. Of course, I had to enter the disk's password just to mount it on the desktop. Disk Utility said the disk was fine other than a few permission issues. I rebuilt the volume directory in TTP, as I usually do after a crash just for precaution, and it didn't report any negative or unusual issues. Then I restarted back to my main partition.

Instead of the usual encryption login screen appearing, I got this:

I added a white box over the login name that was under the icon; it was my username printed there.

This looks like a weird combination login screen of the encryption login and the usual non-encryption login. But I couldn't do anything. I could move the mouse around, but I couldn't click on anything. There was nowhere to type a password. Finally I tried typing the password anyway, and the screen changed to this:

Again, I've whiteboxed the username and now a snippet of other text: my password hint. But you can see around the password hint are rows and rows of colored noise. It didn't change at all -- e.g. it was not video noise -- though if I clicked or pressed a key, it would go away, and then come back with another keypress. This was really confusing. I had just accessed this disk a few minutes earlier! And I'd checked it by booting via another partition, with no problems.

On another computer, I googled possible issues and looked through the Apple support resources. I didn't see any situations quite like this, but I did get the idea to check the encryption. I booted the troubled laptop into Recovery Mode (command-R) and turned off encryption via Disk Utility. After that, the computer booted directly to the usual non-encryption login screen without problems, and worked fine. It took about 3 hours for the system to finish decrypting itself (per the Security preference status) but there were no problems.

After it decrypted, I ran all my disk utilities again (no problems found!) and tried enabling FileVault 2 again. When you enable it, you have to restart. I did that, and... it gave me the same login weirdness described above. EXACTLY the same. So I booted back into recovery mode and disabled encryption again, and everything is working fine (other than not being encrypted as I want).

Does anyone have suggestions for what is going wrong with FileVault 2? Is there a config or preference file somewhere that I can delete or edit? A flag that needs to be set via command line? A disk driver that can be reinstalled without wiping the disk? I do not relish the idea of reformatting the drive and restoring it via Time Machine backups, though I would consider it as a last resort.

Any suggestions will be appreciated. Thanks in advance.