The issue is not just leading backslashes, also backslashes in the middle are not escaped. Or the other way around, only a trailing backslash is escaped.

Another example

Code:

D:\>KIX32.EXE test.KiX $var="\\aa\\bb\\cc\\"
\\aa\\bb\\cc\   <- only the trailing backslash is escaped, I would have expected either \\aa\\bb\\cc\\ or \aa\bb\cc\ as result

D:\>KIX32.EXE test.KiX $var="\aa\bb\cc\"
\aa\bb\cc"      <- only the trailing backslash is escaped