Bottle of French Wine for the Explanation of Data

Albert Theuwissen offers a bottle of good French wine to someone who explains the lack of consistency between gain and exposure settings in his CMOS sensor measurements. One can expect that signals measured at gain=1, exposure=42.24ms and gain=4, exposure=10.56ms are equal. In fact, they are not:

Sensor output value (corrected for the offset) as a function of
measurement number, for each measurement the camera gain
and exposure time are matched to each other.

Same data as above, but now with the regression lines added.