I just downloaded and tried a more recent MSYS2 version: http://sourceforge.net/projects/msys2/files/Alpha-versions/64-bit/x64-msys2-20131022.tar.xz

Unfortunately the described issue keeps the same: A "\=" sequence is only un-escaped if there is some other argument passed to the command using double quotation marks.

Installed program versions are:

$ uname -a
MSYS_NT-6.1 C1255vm 2.0.0(0.270/5/3) 2013-10-18 22:41 x86_64 Msys

$ make -v
GNU Make 4.0.90
Built for x86_64-pc-msys

$ sh --version
GNU bash, version 4.2.45(2)-release (x86_64-pc-msys)

Lars Kanis