SiSoft Sandra has several bugs. And there are not that much people with dual Opteron boards to report these problems. All results shown by SiSoft Sandra should be rated very carefully. SiSoft also reports my FAN speeds too slow and claims that at least one fan fails but all are spinning as they should.
The displayed temperature difference between the first and the second CPU is an effect that all dual-CPU Tyan boards seem to have. I have two identical CPUs and both are cooled with the "boxed" HSF that came with the CPU. They both run at different temperatures.