transtab_latex_unicode sometimes not set in bibtex import

Importing bibtex files, I sometimes get this error in the log:

Invalid argument supplied for foreach() in /var/www/vhosts/xxxx/sites/all/modules/biblio/bibtexParse/PARSEENTRIES.php on line 178.

I determined that the cause was that the PARSENTRIES object property transtab_latex_unicode was sometimes not set. This is loaded in the constructor function via a require_once include (line 141).

I'm not sure why this could not be a class property, but as a workaround to the current implementation I found that changing the require_once to a require eliminated the problem.

--- sites/all/modules/biblio/bibtexParse/PARSEENTRIES.php	(revision 1169)
+++ sites/all/modules/biblio/bibtexParse/PARSEENTRIES.php	(working copy)
@@ -138,7 +138,7 @@
    */
   function PARSEENTRIES()
   {
-    require_once(drupal_get_path('module', 'biblio') . '/bibtexParse/transtab_latex_unicode.inc.php');
+    require(drupal_get_path('module', 'biblio') . '/bibtexParse/transtab_latex_unicode.inc.php');
     $this->preamble = $this->strings = $this->undefinedStrings = $this->entries = array();
     $this->count = 0;
     $this->fieldExtract = TRUE;