“**C\Program Files*" is for 64-bit apps and plug-ins.
"**C:\Program Files (x86)*” is for 32-bit apps and plug-ins.
Audacity is a 32-bit app on Windows and can only use 32-bit plug-ins. 64-bit plug-ins won’t work in Audacity on Windows.
Yes Audacity “should” find VST plug-ins that are in the VST Path (when they are supported plug-ins).
I’m not able to test this as I’m on Linux, but I’ll ask the developers if they can reproduce the problem.
Yes this is a bug. I’ve logged it on the Audacity bug tracker.
As a workaround, the plug-in, or a copy of the plug-in can be placed into:
32-bit Windows:
C:\Program Files\Audacity
or
64-bit Windows:
C:\Program Files (x86)\Audacity