OK, here's the log after I double tapped:
Oct 22 16:31:22 --- last message repeated 62 times ---
Oct 22 16:31:31 localhost kernel[0]: ps2: dx=0, dy=0 (1517,4193) z=37 w=5 mode=(0,0,1) buttons=0 wasdouble=0
Oct 22 16:31:31 localhost kernel[0]: ps2: dx=-2, dy=0 (1515,4193) z=45 w=5 mode=(1,1,1)...