I cannot reproduce you finding here on 5.14 built for Vista 64-bit:

C:\test\perl-5.14.0-RC1>.\perl -V
Summary of my perl5 (revision 5 version 14 subversion 0) configuration
+:

  Platform:
    osname=MSWin32, osvers=6.0, archname=MSWin32-x64-multi-thread
    uname=''
    config_args='undef'
    hint=recommended, useposix=true, d_sigaction=undef
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=und
+ef
    use64bitint=define, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cl', ccflags ='-nologo -GF -W3 -MD -Zi -DNDEBUG -Ox -GL -fp:pr
+ecise -
    optimize='-MD -Zi -DNDEBUG -Ox -GL -fp:precise',
    cppflags='-DWIN32'
    ccversion='15.00.21022.08', gccversion='', gccosandvers=''
    intsize=4, longsize=4, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=undef, longlongsize=8, d_longdbl=define, longdblsize=8
    ivtype='__int64', ivsize=8, nvtype='double', nvsize=8, Off_t='__in
+t64', l
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='link', ldflags ='-nologo -nodefaultlib -debug -opt:ref,icf -lt
+cg  -li
    libpth=\lib
    libs=oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.lib  
+comdlg3
    perllibs=oldnames.lib kernel32.lib user32.lib gdi32.lib winspool.l
+ib  com
    libc=msvcrt.lib, so=dll, useshrplib=true, libperl=perl514.lib
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_win32.xs, dlext=dll, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags='-dll -nologo -nodefaultlib -debug -opt:
+ref,icf


Characteristics of this binary (from libperl):
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_IMPLICIT_SYS
                        PERL_MALLOC_WRAP PERL_PRESERVE_IVUV PL_OP_SLAB
+_ALLOC
                        USE_64_BIT_INT USE_ITHREADS USE_LARGE_FILES
                        USE_PERLIO USE_PERL_ATOF
  Locally applied patches:
        RC1
  Built under MSWin32
  Compiled at Apr 21 2011 08:07:59
  @INC:
    C:/test/perl-5.14.0-RC1/lib
    .

C:\test\perl-5.14.0-RC1>.\perl.exe -E"print pack 'Q', 1 "
☺
C:\test\perl-5.14.0-RC1>.\perl.exe -E"print length pack 'Q', 1 "
8
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