If parts of $PATH have spaces in them, then the shebang handling breaks. For example, when I try to exec a script with #!/bin/sh on my system, I get an error about how it can't find "Files\TheVeeb\bin\sh.exe" since it has lost the part before the space C:\Program
Win-bash is no longer under active development. So I am sorry, but we have to close this as a wont-fix.