For certain loads, it seems the values in the apparent, active and reactive power registers do not obey the relationship S^2 = P^2 + Q^2.
Load 1 (fan):
S (apparent): 169891
P (active): 167197
Q (reactive): 29829
sqrt(P^2 + Q^2) = 169836, very close to the expected apparent power
Power factor: 0.98
Load 2 (LED lamp powered by a SMPS):
sqrt(P^2 + Q^2) = 37468, only 60% of the apparent power register value
Power factor: 0.58
Load 3 (same lamp at a higher brightness):
sqrt(P^2 + Q^2) = 136012, 67% of S
Power factor: 0.65
Why would this be? For the values to be meaningful, the above relationship must certainly hold for the real units (expressed in VA/W/var) and I think it should also hold for the LSB values, as the conversion factor from LSBs to real unit should be the same or very similar for all three registers.
Have I made a stupid mistake, or are the values I'm getting incorrect?