I assume you're talking about the adjustable cup. I had the same problem. Although, I don't understand why it was happening. Inspected the threads, on both the cup and the bracket, they were both fine. Cleaned, re-packed, re-greased, noticed the same problem on assembly.

Then I figured I would draw upon my ghetto Naval fixes of the past (as I'm sure you're experienced with William). I put ONE layer of Teflon tape on the inside of the cup. Grease on the outer portion. It threaded on perfectly....and no longer moved within the bottom bracket.

I thought the movement was causing a metal-on-metal sound when I pedaled. It ended up being chainring bolts.

I don't know if this is a solid fix. My little book-o-bike repair says that they usually use Teflon tape on Titanium bottom brackets. It's worked like a champ on my steel Tommasini.