This shows c: and d: prefixes in the same message evaluation.
I haven't mentioned yet that I don't have a D drive mounted at all.
I tried C-h v source-directory in a running Emacs and found:
source-directory is a variable defined in `lread.c'. Its value is "d:/devel/emacs/release/emacs24/emacs-24.2/"
Documentation: Directory in which Emacs sources were found when Emacs was built.
You cannot count on them to still be there!
I did not find this /devel/emacs/release/emacs24/emacs-24.2/ on my system, nor is it the kind of path I would create. My emacs is at C:\Users\epich\sw\emacs-24.2 which appears in Cygwin at ~/sw/emacs-24.2 because ~/sw symlinks (MS console command mklink /d) to /cygdrive/c/Users/epich/sw .
I actually launch Emacs from the Quick Launch on Windows 7, so the C-h v evaluation has Cygwin out of the equation. I merely use Cygwin to byte compile.