According to the docs, $t->cmd_remove_mode(1) removes one line to be echoed. Is it possible the remote host is returning 2 lines, the first of which you are correctly suppressing but the second line is still echoed? Could you try setting cmd_remove_mode to 2 to see if that makes any difference?

$t->cmd_remove_mode(2); # so that we suppress two lines
my @distro = $t->cmd(String => "cat /etc/redhat-release");
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Also, check out the possibility of using option_accept()