It looks like your C-runtime libraries or Perl implementation is broken(1).

I cannot reproduce your results on my platform:

<Reveal this spoiler or all in this thread>

The only logical thing for CLONE to do for an open filehandle is dup() or dup2(), and according to the man pages for those calls: 

NAME
       dup, dup2 - duplicate a file descriptor

SYNOPSIS
       #include <unistd.h>

       int dup(int oldfd);
       int dup2(int oldfd, int newfd);

DESCRIPTION
       dup and dup2 create a copy of the file descriptor oldfd.

       After successful return of dup or dup2, the old and new descrip
+tors may
       be used interchangeably.

[download]
They share locks, file position pointers and flags; for example, if the file position is modified by using lseek on one of the descriptors, the position is also changed for the other.

       The two descriptors do not share the close-on-exec flag, howeve
+r.

[download]

1. That is, your platform is exhibiting unspecified--thought clearly defined--behaviour.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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In the absence of evidence, opinion is indistinguishable from prejudice.
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In reply to Re^3: Threads: How to share a FileHandle to Write by BrowserUk
in thread Threads: How to share a FileHandle to Write by gulden

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