I don’t know who fixed this, or how but I just updated to Windows 8.1 and besides obvious UI improvements, such as the store etc., and online account management, the OS itself is far more stable and responsive (albeit I had to drop some cheap USB devices) however additional memory is consumed but obviously this is the way forward for Windows users.
The previous issue of not being able to solo more than one part when Edit Active Part is used, i.e. to select a note within a selection of parts; actually soloed the instrument. Having to mute parts in the project window preemptively was a real pain but now it’s all fixed on Windows 8.1.
P.S. Next time when something like this happens, SB should email all effected persons. Any thanks for discovering this should be directed to myself.