I am preparing the astronomical ephemerides of the year 2018 for my astronomy club. According to my information, comet 46P / Wirtanen is expected to have a peak of brightness in December 2018, reaching magnitude 3.8. However, Kstars indicates that its magnitude would reach 7.43 on December 15 instead of expected 3.8. In addition, the coordinates given by kstars differ from those given by skychart or stellarium. I have yet updated my comets orbital elements.
How to explain these differences? Before submitting a possible bug, can someone confirm that the information of 46P / Wirtanen given by Kstars are incorrect for December 15, 2018?