GNU diff -x on win does exclude patterns with back slash (\) or slash (/)

[yzz]

Hi,
Using 2.7-cygwin-990830 on Win XP SP2
having problems running a directory comparison with excluded paths if
the exclude path involves using back slash
for example if i run
diff -u -q -r -x foo.c <src path> <dest path>
(foo.c is missing from the sub-folder bar that is under dest)
foo.c get excluded
but if I run
diff -u -q -r -x bar\diff.c  <src path> <dest path>
foo.c does not get excluded

Thanks