Hello Jacques.

I can't be of much help, I'm sorry, but I think this might be by design, and not a bug. I do know that Firefox 4's inbuilt sync won't have a constantly displayed status icon, so that might be just how they updated the extension, to work like it will work on Firefox 4. All in all, it shouldn't be necessary for the user to constantly check if its browser is synced. It should always be.

Having a visual display of the sync status has its advantages

I'm sure it does. If you want to argue about that, you're more than welcome to use this group: http://groups.google.com/group/mozilla.dev.usability

Please do, as user input is always appreciated.