Not sure how useful this is but under AS 5.6.1 and 5.8 the seek & tell don't seem to be necessary.

Totally speculation: Could this be a useperlio thing. This is undef in both the AS builds.

C:\test>type test.pl
#$a = tell(DATA);
#seek(DATA,$a,0);

open(STDIN, "<&DATA");
while(<STDIN>){
  print "STDIN: $_";
}
__DATA__
Foo
Bar
Quux

C:\test>test
STDIN: Foo
STDIN: Bar
STDIN: Quux

C:\test>copy test.pl test.pl8
        1 file(s) copied.

C:\test>test.pl8
STDIN: Foo
STDIN: Bar
STDIN: Quux

C:\test>
[download]