Why do you close STDOUT. You can use select instead.
I don't see why you use seek in your code when you open one filehandle for input and one for output. If you whould have used +> instead, you would need the seek. (see perldoc perlopentut).

use POSIX;
use strict;

my $TRAP=POSIX::tmpnam();
print "TMPFILE is $TRAP\n";

open(TMPFILE, "+> $TRAP") or die $!;
select TMPFILE;
eval { print 'Waka Waka' };
seek(TMPFILE,0,0);
my $input=<INFILE>;
close(INFILE>;
select STDOUT;

print $input;
[download]

This works fine for me.
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Dr. Mark Ceulemans
Senior Consultant
IT Masters, Belgium