I did not check that, and it did not start anything once I plugged the drive back in. I just wanted to make sure it was mirroring correctly, which it is.
The WD literature states that once you replace a faulty caviar green drive with a fresh one, to not access the drive for 12 hours so it can rebuild. Maybe it will only initiate the rebuild if you plug in an unformatted blank drive.
I am not too worried about the rebuild process, as long as its mirroring correctly.