Position angle in different time

I found the configuration for PA=0 deg. did not look like PA=0. I ran the code as follows:

./ets_demo assigner=naive input=ets_test_data.dat fract=0.90 output=tmp.out ra=34.0 dec=-4.5 posang=0.0 dposang=0.0 nposang=1 dptg=0.0 nptg=1 time=2016-11-09T08:00:00Z

"ets_test_data.dat" can be found here:
http://member.ipmu.jp/kiyoto.yabe/tmp/ets_test_data.dat

Using the coordinate of allocated objects, the PFI FoV looks rotated against the north direction, and this tilt angle seem to depend on the observing time set. What kind of effect is this from?