I do not know if it is suppose to be this way, but,
a) On multiple occasions I was able to co-locate my unit with the monster unit and stay in the same squere for quite long time.
Sometimes not mine units are flickering. In the begining of the turn they appear for like 0.5s and then disapear. What's interesting it is true even if they are in the explored part of the map where I do not have LOS.