Firmware Update 1.02 solves problem...
There was a thread some time ago about the D7000 semi-shutting down, with AF stopped if you accidentally touched the lens release button when the camera was on.
I noticed this intermittently with my Sigma 8-16 and 50/1.4, even after uploading 1.01.
Since uploading the new firmware (1.02), this problen cannot be duplicated, at least not on my camera body. I can try to trigger the issue, to no avail. I wonder if the new firmware has addressed this... On my D7000 it appears to have done so.
#2. "RE: Firmware Update 1.02 solves problem..." | In response to Reply # 0