Zend_Barcode_Object_ObjectAbstract contains:

.   /**
     * Set text to encode
     * @param string $value
     * @return Zend_Barcode_Object
     */
    public function setText($value)
    {
        $this->_text = trim($value);
        return $this;
    }

But in barcode Code39 standard there is ' '(space) char available. Problem appears when space is at the and of barcode text. In this function trim remove this char.

Solution:

Override setText in Zend_Barcode_Object_Code39 by removing trim:

.   /**
     * Set text to encode
     * @param string $value
     * @return Zend_Barcode_Object
     */
    public function setText($value)
    {
        $this->_text = $value;
        return $this;
    }