Finally, I have worked out a fix - although I am not 100% sure of the details.
*** ONLY DO THIS IF YOU ARE AN EXPERIENCED USER AND UNDERSTAND THE RISKS OF
WORKING WITH THE REGISTRY ***
I had another (local) account on my machine which did show the Extended
Tiles ok, so I looked at the various areas where SyncMgr was in the registry
on this machine, especially those in the HKCU, and found a section which
looked hopeful. With a but of trial and error (backing up registry, etc. to
make sure it did not cause other problems) I found that there was a registry
entry somewhere in the are
HKEY_CURRENT_USER\Software\Classes\Local
Settings\Software\Microsoft\Windows\Shell
which had been corrupted - by copying these across to the user I was having
the problem with, it reinstated the Extended Tile in Sync Manager.
Not sure which registry key was the cause of this, and now I'm back up
working, will not be looking at this in more depth, so I hope that this helps
someone else in a similar position - and allows them to identify the exact
key (if so, please can they add this into the thread).
So, in terms of fixing this problem (losing the Extended Tiles on Sync
Center):
1. First try using the Reset Folder option in the View Tab of Explorer's
Tools/Folder Options.
2. If still not fixed, try System Restore to see if this resolves the issue.
3. If still stuck, and you have another user on the machine which does work
ok, they look at the registry area above and maybe do a compare of the files
to see what is missing.
As always, if making changes to the registry, make sure you have a backup
before the changes (or at the very least a System Restore point) and be very
very careful, as changes to the registry can cause system instability, etc.
etc.