I found the problem to be a missing code line (2.8.3).
Apparently, in comments.php (Dashboard -> Appearance -> Editor -> comments.php) there is the following check line:
<?php if ( !empty($comments_by_type['pings']) ) : ?>
Testing it, I found that the $comments_by_type variable is NOT SET, hence the IF check will fail and trackbacks and pingbacks won’t show.
To fix this, just add the following line BEFORE the line above:
<?php $comments_by_type = &separate_comments($comments); ?>
This simply sets the $comments_by_type variable with the necessary info for the loop to take on pings and trackbacks.
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Basically it should look like this:
<?php $comments_by_type = &separate_comments($comments); ?>
<?php if ( !empty($comments_by_type['pings']) ) : ?>
instead of
<?php if ( !empty($comments_by_type['pings']) ) : ?>
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Let me know if this has helped you guys out with your versions.
Cheers,
Mike