CPU affinity is not working as expected (by me

) on dual Xeon E5-2460v3 on Windows 2012 R2
I want to use only 1 thread per physical core on both the CPUs, but I'm not able to do it.
I'm testing v3.7.9 with the following cmd line:
cpuminer-aes-avx2 -a lbry -t 16 --cpu-affinity 0xAAAAAAAA [...]
I'd like to spread the threads over the 16 available physical cores, but I'm only able to saturate 16 logical processor of the first CPU:
http://i68.tinypic.com/saupo5.pngNo matter what I set in the affinity option, I always obtain the same result.
If I start cpuminer with "-t 1" I get 526 kH/s per CPU, when I start it with "-t 16" I obtain only 249 kH/s per CPU.
On a single CPU system with 8 cores and 16 logical cpu, I'm able to obtain exactly what I want with affinity.