Drift in "Linear Acceleration in World"

Hi, I'm trying to understand the results I get back from inv_get_linear_acceleration_in_world(). Using the motionFit SDK, and with it just sitting on my desk, after powering it up and never touching it, I typically get this kind of a reading value:
linear world: 0.00073 -0.00146 0.80933

If I run the inv_self_test_calibration_run(), I will then get results that typically look like this (which is what I would expect, all of the x,y,z values very close to zero):
linear world: -0.00049 -0.00269 -0.00122

But, if after I run the calibration self test, I even tap the sensor on my desk very lightly, it will switch to and hold a value within a few hundredths of these values shown here:
linear world: -0.00049 0.00000 -0.10181

I would expect that z axis to be a lot closer to zero when there is absolutely no motion on the device. Is that the appropriate expectation? Is there some additional calibration I should need to do? I get this in both 6-axis and 9-axis sensor mode - but I am primarily interested in fixing this in the 6-axis mode.

Thanks