I'm one of the monks who went over this with sgifford in the Chatterbox (davido is the other), I'm completing sgiffords question with some of the findings in the chatterbox. We've established the following:

1. Code works as is, in perl 5.8.7
2. Code works with perl 5.6.1 provided you replace the $f1 with an actual globale handle, like F1:

   tie *F1, 'TieTest';
   print "Read: ",scalar(<F1>);
   [download]

3. Replacing the gensym with an instance of IO::Handle doesn't make a difference (that's why the line use IO::Handle is in this code).
4. Opening $f1 first to a different handle in order to make the handle exist in the glob, doesn't help.

We're all very curious to what is going on, and if there's a way around it apart from upgrading Perl. I personally suspect that there's a problem with autovivification of the filehandle with the tie, but it's just a suspicion.

Any insight from somebody who really knows what is going on, and preferably, a way to make it work on perl 5.6.1, would be appreciated.

Update I've now had a chance to test it on Indigoperl (Activeperl compatible) 5.6.1 on Win32: I can confirm it has the same problem there. It looks like an actual bug in 5.6.x to me.