Michel,
I have been using a UPS protected power supply for my ISY 99ir Pro for several months. Because a 'whole house' surge protector is installed, it is not clear whether or not the system has experienced significant surge loads, but we have had several short power outages which would have affected the PLM which is, of course, not on the UPS. To date no problem has been encountered with the PLM re-establishing communication with the ISY after power is restored and without human intervention.
Doug