I think the listed twice problem is linked with the disappearing add ins.viewtopic.php?f=6&t=63605
It effected all add-ins including add-in that were installed and working ok - just not being listed.
If I re-installed the add in it got listed twice.
The same with new add ins.
It appeared for me on a 1462 to 1463 debug non-portable upgrade.
I cannot reproduce now because I am now on a 1464 portable install
Running MM on 32 bit Vista as administrator.