hmm... i thought the AMD CPU's only show one core temperature, how are you seeing two? what CPU do you have? are you sure the 70C isnt your actual CPU temp and the 50C being the MB/Case temp?
Ah that could be it! Or the 50C is the "socket temp" I know for my CPU in HWMonitor and SpeedFan there's the core temps and then the CPU temp which is always significantly lower.