How to stop duplicate Safari bookmark folders

With iCloud set to sync Safari bookmarks on our iPhone, MacBook Pro and iMac 20", Safari is making numerous duplicate copies of of the BookmarkMenu and BookmarkBar folders - so many, in fact, that it can take a minute or so just to delete them all.... and then they all return with the next sync.

I've tried turning off iCloud bookmark syncing and re-creating the bookmarks on the MacBook Pro and this works fine. I then erase ALL bookmarks on the other devices so NO devices have duplicates. Then I turn syncing back on and all my devices get the duplicates. 😠

I'm wondering whether the bookmarks in iCloud are corrupted but can't see anyway of erasing them. It was easier with MobileMe as you could 'replace on MobileMe' the original data.

Has anyone got any ideas on how to fix this? It's so frustrating...