Extra fields are nicely lined in a list. And "even" and "odd" are added as classes to each line. Unfortunately this does not work well as soon as some of the fields are ommitted because they are empty.
The reason is the code in .\components\com_k2\templates\default\item.php, around line 254:
<?php foreach ($this->item->extra_fields as $key=>$extraField): ?>
<?php if($extraField->value != ''): ?>
<li class="<?php echo ($key%2) ? "odd" : "even"; ?> type<?php echo ucfirst($extraField->type); ?> group<?php echo $extraField->group; ?>">
Fix (whole <ul>):
<ul>
<?php $evenodd = 0; foreach ($this->item->extra_fields as $extraField): /* RL130301 $evenodd added */ ?>
<?php if($extraField->value != '') { $evenodd++; ?>
<li class="<?php echo ($evenodd%2) ? "odd" : "even"; ?> type<?php echo ucfirst($extraField->type); ?> group<?php echo $extraField->group; ?>">
<?php if($extraField->type == 'header'): ?>
<h4 class="itemExtraFieldsHeader"><?php echo $extraField->name; ?></h4>
<?php else: ?>
<span class="itemExtraFieldsLabel"><?php echo $extraField->name; ?>:</span>
<span class="itemExtraFieldsValue"><?php echo $extraField->value; ?></span>
<?php endif; ?>
</li>
<?php } ?>
<?php endforeach; ?>
</ul>