In particular UNC (\\SERVER\FILE) style names are problematic in 1.23. As soon as direct passing of filenames to gpg are enabled the extra quoting done in w32-io.c and gpgme-w32spawn.c is misbehaving. Probably due to the double quotes using in UNC.
Instead of fixing these nasty double-backslash things and risking other breaks of quoting (again), we should pass forward slashes to gpg. This is well defined for Windows just a bit common for Windows-only users.
See also rM0221d7f28a315d305409cf2dcae853c22ad94d31