This is a serious bug in Win32::FileSecurity. In FileSecurity.xs, Set iterates over the passed hash (reference) and then does this on the key:

        if ( lpszTemp = strchr( lpszAccount, '\\' ) ) {
            lpszServer = lpszAccount ;
            *lpszTemp = '\0' ;
            lpszAccount = lpszTemp + 1 ;
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(It does this in order to call LookupAccountNameA((LPCSTR) lpszServer, (LPCSTR) lpszAccount, ...).

This is just wrong. Please file a bug report at http://rt.cpan.org/NoAuth/Bugs.html?Dist=libwin32.

Hashes share key values, which is how this affects the other hashes. I don't see any workaround for this without fixing Win32::FileSecurity.xs