Boomarks Replaced Somehow

Hi folks.

For some reason I had to bring back a historical Safari bookmarks (~/Library/Safari/bookmarks.plist) through Time Machine. The bookmarks change upon quitting Safari and re-opening Safari. About a day later, the bookmarks go back to the problematic collection.

It's driving me crazy as I've replaced it with a good set about 6 times now and it keeps going back. How can I fix this?

Cheers