But soon I started to notice serious heating problems from time to time at the upper part where the GSM chip is located, accompanied by quick battery drain (from 90%+ to 15% in a few hours, without doing anything but a few calls and some email checking).
I changed max speed from 4G to 3G and stopped all background tasks, disabled tap&send, but nothing made any noticable difference.
Then I noticed on my Femto Cell (a mini in-hous GSM transceiver) the 'connected' light was on while my phone had a working WiFi connection at the same time. This indicated that the GSM was on while I had a WiFi connection. Only rebooting the phone would disconnect the 3G and use just WiFi. But after some time and using the phone, the 3G connection would come back on (light on the Femto Cell turns on) and the heating and draining would start again.
This looks to me like a serious bug in my (hardware revision 22.214.171.124) Lumia 920!
Anyone else experiencing this with the Black update?