Are you on Win32 by any chance? I've seen this documented in perlport: 

As an optimization, may not call the command shell specified in
$ENV{PERL5SHELL}. "system(1, @args)" spawns an external process
and immediately returns its process designator, without waiting
for it to terminate. Return value may be used subsequently in
"wait" or "waitpid". Failure to spawn() a subprocess is
indicated by setting $? to "255 << 8". $? is set in a way
compatible with Unix (i.e. the exitstatus of the subprocess is
obtained by "$? >> 8", as described in the documentation).
(Win32)

[download]

-xdg

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In reply to Re: system() not quite as described? by xdg
in thread system() not quite as described? by jdtoronto

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