It appears that NEC has finally received enough complaints on this problem and has opened a ticket with Japan. In the meantime it seems that the problem appears more related to the type of phone the EHS is connected to. We don't seem to have a problem with the headsets on 12/24 button, seems more of a problem with the desi-less phones only. I'm going to one of our customers with a chronic problem and we are going to temporarily replace the desi-less with a 12 button.