Computed field incorrectly computed.

The taxonomy handling is a bit tricky. When editing nodes, the taxonomy is in one format, and when re-computing it is in a different format. The code below should do the trick. It might not fit your needs excactly, bu it should give you the basic idea :)

  // Set given terms by node language
  // We have different vocabularies with the same role for each langauge...
  $vids_by_name_and_language = array(
    'term_section' => array(
      'da-DK' => 1,
      'sv-SE' => 10,
    ),
    'term_category' => array(
      'da-DK' => 2,
      'sv-SE' => 3,
    ),
  );

  // Teaser terms. Set the terms by language.
  // This has to take into account both different vids by language and the built in
  // messed up handling of terms when saving nodes and recomputing nodes, so thats why
  // it might seem a bit messy...
  if (!empty($node->taxonomy) && !empty($node->language)) {
    $taxonnomies_to_save = array_keys($vids_by_name_and_language);
    // Just grap the first comming term of given vid...
    foreach ($node->taxonomy as $key => $term) {
      // The node is just beeing re-computed with the re-compute field
      if (is_object($term)) {
        foreach ($taxonnomies_to_save as $name) {
          // Check to see if we have a vid to check on.
          if (empty($vids_by_name_and_language[$name][$node->language])) {
            continue;
          }
          $vid = $vids_by_name_and_language[$name][$node->language];
          if ($term->vid == $vid) {
            $teaser_values[$name . '_tid'] = $term->tid;
          }
        }
      }
      // The node is being created or updated, and the $key is not the vid...
      elseif (is_array($term) && !empty($term)) {
        foreach ($taxonnomies_to_save as $name) {
          // Check to see if we have a vid to check on.
          if (empty($vids_by_name_and_language[$name][$node->language])) {
            continue;
          }
          $vid = $vids_by_name_and_language[$name][$node->language];
          if ($key == $vid) {
            // Just grap the first term.
            $tid = current($term);
            if ($term_loaded = taxonomy_get_term($tid)) {
              $teaser_values[$name . '_tid'] = $term_loaded->tid;
            }
          }
        }
      }
      elseif (is_string($term) && !empty($term)) {
        // The node is still being created or updated, but we only have one term.
        foreach ($taxonnomies_to_save as $name) {
          // Check to see if we have a vid to check on.
          if (empty($vids_by_name_and_language[$name][$node->language])) {
            continue;
          }
          $vid = $vids_by_name_and_language[$name][$node->language];
          if ($key == $vid) {
            // Just grap the first term.
            if ($term_loaded = taxonomy_get_term($term)) {
              $teaser_values[$name . '_tid'] = $term_loaded->tid;
            }
          }
        }
      }
    }
  }

From the README.txt:
"Please note that when you re-compute the nodes, the node is fetched through node_load() which means that the format of some values might defer from when you submit the node through the node edit form. $node->taxonomy does this."

This is not a bug. This is just the way is has to be. The alternative would be, that I had to emulate a node submit which would in my opinion be a rather more messy solution with many potential pitfalls.

Another work around is to not use the use $node->taxonomy but to get the terms via taxonomy_node_get_terms in the computed field. This will work in both the edit form and in re-compute and in a views bulk operation.

edit: oops, I see this code will only work in D6. However, I think something similar can be done in D7.

$vterms = taxonomy_node_get_terms($node);
$vitems=array();
foreach ( $vterms as $vterm ) {
        $vitems[]=$vterm->name;
    }

$node_field[0]['value'] =implode(", ", $vitems);