[otrs] Update response time, don´t update

Hi everybody, win 7 / mysql / otrs3.1.12 / itsm 3.1.7 I'm using service & sla and defined first response, update and solution time, but when I create a phone ticket and the sla is asigned and ticket created, only first response and solution time are stopped with some action, like external note or close without problem. But with the update time I can´t find how to comply, because each article like a new external note or priority update or queue update, the update time is restarted!! Someone could help me? I appreciate so much your help Antonio