This seems like an interesting bug to me, both 5.6.1 and 5.8.0-pre affected. Look (I've condensed your test case a bit for use it from a single file): 
package Foo;
sub TIEHANDLE { bless {}, $_[0]}
sub READLINE {return "foobar\n"}

package main;
#use Foo;
tie(*TEST, Foo);
chomp($data = <TEST>);
print join(", ", map { ord($_) } split(//, $data)) . "\n";
chomp($data);
print join(", ", map { ord($_) } split(//, $data)) . "\n";

[download]
results in strange output 
102, 111, 111, 98, 97, 114, 10
102, 111, 111, 98, 97, 114

[download]
but following: 
package Foo;
sub TIEHANDLE { bless {}, $_[0]}
sub READLINE {return "foobar\n"}

package main;
#use Foo;
tie(*TEST, Foo);
chomp($data = <TEST>, $data);
print join(", ", map { ord($_) } split(//, $data)) . "\n";
chomp($data);
print join(", ", map { ord($_) } split(//, $data)) . "\n";

[download]
and even 
package Foo;
sub TIEHANDLE { bless {}, $_[0]}
sub READLINE {return "foobar\n"}

package main;
#use Foo;
tie(*TEST, Foo);
chomp($data ||= <TEST>);
print join(", ", map { ord($_) } split(//, $data)) . "\n";
chomp($data);
print join(", ", map { ord($_) } split(//, $data)) . "\n";

[download]
produce expected output: 
102, 111, 111, 98, 97, 114
102, 111, 111, 98, 97, 114

[download]
My intuition says to me that it's not because of implementation of tied filehandles is incomplete, but something with a deeper level of strangeness.
Hmm... I think I'll post this to perl5-porters list.

Courage, the Cowardly Dog.

In reply to Re: Tied filehandles and chomp by Courage
in thread Tied filehandles and chomp by nmueller

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