You could set:

my $obj = Net::Telnet->new(
    ...
    dump_log => 'dump.log',
    ....
}

# or

$obj->dump_log('dump.log');
[download]

on your Net::Telnet object to get a "binary" log file showing all the hex characters of what's on the wire - then you could see any funky escape characters in the prompt as suggested by RMGir above.