Illegal offset type in isset or empty in select.inc on line 510

This error occurs only when webform uses "select_or_other" feature.
Steps to reproduce:

1. Create multi-page webform (at least 3 pages).
2. Use mixture of select components on each webform page, some with select_or_other some without it.
3. Now fill form's page 1 and page 2.
4. On page 3 click "< Previous Page".
5. The error occurs.

Now, although the error message relates to select.inc from webform module, the issue occurs only when select_or_other is used. This is the function from select.inc

function _webform_submit_select($component, $value) {
  // Build a list of all valid keys expected to be submitted.
  $options = _webform_select_options($component, TRUE);
  
  $return = NULL;
  if (is_array($value)) {
    $return = array();
    foreach ($value as $key => $option_value) {
      // Handle options that are specified options.
      if ($option_value !== '' && isset($options[$option_value])) { // <==== This is the line where error is thrown
        // Checkboxes submit a value of FALSE when unchecked. A checkbox with
        // a value of '0' is valid, so we can't use empty() here.
        if ($option_value === FALSE && !$component['extra']['aslist'] && $component['extra']['multiple']) {
          unset($value[$option_value]);
        }
        else {
          $return[] = $option_value;
        }
      }
      // Handle options that are added through the "other" field. Specifically
      // exclude the "select_or_other" value, which is added by the select list.
      elseif ($component['extra']['other_option'] && module_exists('select_or_other') && $option_value != 'select_or_other') {
        $return[] = $option_value;
      }
    }
  }
  elseif (is_string($value)) {
    $return = $value;
  }

  return $return;
}

I tried to do some debugging and it seems that select_or_other module changes one of $value array elements from string to array of strings. On line 510 webform expects that $option_value to be a string but it seems that select_or_other turns that string into array of strings.

I tried to fix that but I'm not familiar with webform API and got totally lost.

Aside from error on line 510 of select.inc, when you click "< Previous Page" the values from previous selection are not checked by default, but instead "Other" field is active and all values, comma separated, are put there.