https://bugs.winehq.org/show_bug.cgi?id=49840
--- Comment #8 from Zebediah Figura z.figura12@gmail.com --- Win32 volumes can be mounted to folders other than drive letters; this can be done from diskmgmt.msc. The attached patch, in a manner of speaking, maps Unix mount points to Win32 mounted folders, because the concepts match up quite nicely.
It is not particularly surprising that Windows programs don't account for mounted folders; it seems they are quite a little-known feature. On the other hand, simply ignoring filesystem boundaries doesn't particularly help us; one example of this is bug 38114.