Unfortunately, following master factory reset, restarting randomly has happened again several times on different occasions: browsing google maps, downloading from the Market, etc...
The last thing i've noticed (never had that in the past though) is that when connecting it to the PC through the USB for charging... it triggered a restart. Disconnecting it after restarting it worked fine again, but then trying to charge it through PC/USB caused a restart.
Finally i've managed to charge it without restarts: set it to airplane mode, and it's charging now with no problems.
Fed up with this phone! Tomorrow is its last day. Will take it back for replacement!