Monatsbezeichnungen werden in Statistik doppelt angezeigt

$sql = "SELECT		COUNT(*) AS count, 
					DATE_FORMAT(CONVERT_TZ(FROM_UNIXTIME(".$this->types[$this->type]->dateFieldName."),@@session.time_zone,'+00:00'),'".$sqlDateFormat."') AS groupBy,
					MAX(".$this->types[$this->type]->dateFieldName.") AS date
			FROM		".$this->types[$this->type]->tableName."
			WHERE		".(($this->userObj !== null && $this->types[$this->type]->userFieldName) ? $this->types[$this->type]->userFieldName." = ".$this->userObj->userID." AND" : '')."
					".$this->types[$this->type]->dateFieldName." > ".$fromDate."
					AND ".$this->types[$this->type]->dateFieldName." < ".$untilDate."
			GROUP BY 	groupBy
			ORDER BY	".$this->sortField." ".$this->sortOrder;
		$result = WCF::getDB()->sendQuery($sql);
		while ($row = WCF::getDB()->fetchArray($result)) {
			$results[] = $row;
			if ($row['count'] > $max) $max = $row['count'];
		}