We're very sorry for the delay in response. It took a bit of hunting around to reproduce this issue on our test site as we had a hard time getting the category added to the link. Once we enabled the option in K2 settings > Advanced > Advanced SEF Settings > 'Enable advanced SEF for K2 URLs', we had similar as you're describing in your first post.
I think it should be a small change of code.
1. Could you verify that you have the 'Enable advanced SEF for K2 URLs' option enabled?
2. Could you try replacing /plugins/opengraph/k2/k2.php at line 438
$link = 'index.php?option=com_k2&view=item&id='.$item->id;
with
require_once(JPATH_SITE . '/components/com_k2/helpers/route.php');
$link = K2HelperRoute::getItemRoute($item->id . ":" . urlencode($item->alias), $item->catid);
Let us know whether this helps to resolve your issue or if you continue to have incorrect autopost URLs.
Thanks
-Melissa