Replace Windows Defrag?

I like the option to replace the default defrag utility in Windows XP with defraggler. I had it setup to defrag every night, while I slept.

Well, not sure if it was a defraggler update or a windows update but it seems the MS defrag has been put back into its place.

The option to reset Defraggler as a replacement for defrag is grayed out.

If this is a bug, and a workaround available I'd love to hear it.

If it's intentional, please add that option back. :)