WordPress meta-box and checkbox-list

The issue is probably with the $single parameter of get_post_meta function. Try setting it to false or delete it. Codex Link

Then, 

$omc_os_poker_room =  get_post_meta(get_the_ID(), 'omc_os_poker_room');
    echo '<p class="omc-info-one"><b>OS: '.$omc_os_poker_room[1].'</b>';

Not tested, but should work.

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