Adding an unofficial library and browsing for:
C:\Users\Public\Documents\LDraw\Unofficial\ (which is my actual unofficial library)
I get the following pop-up:
"This is not a valid LDraw library, use it anyway?"
Which is misleading 'cos it IS a valid library, "unofficial" but valid. This is even more misleading as I obviously don't get such a pop-up when I select the parent:
C:\Users\Public\Documents\LDraw\
w.
LEGO ergo sum