To evaluate various problems listed below I made a hotkey to "cycle next enemy". Using this hotkey every 2 seconds or so in an area having live (currently active) spawn(s) of mobs, and noting that according successive targeted mobs are shown in the target window at increasing distance - usually no greater than 200 meters before restarting the cycle beginning with the nearest mob - and thus I concluded that the intended maximum targeted mob range is currently 200 meters.
Repeated cyclying of the mobs occasionally "targets" a mob at greater than 200 meters and typically this target range slowly increases - in some cases up to as much as 2000 meters or more. This is bug #1.
To illustrate bug #2, cast a spell while the target window is showing a mob at range greater than 200 meters. The spell indeed triggers as expected by virtue of the mob being in the target window, but does not cast because the target mob is out of range and the game feedback message is "out of range" by a number of meters always less than 200.
Now simply wait until the target window goes blank and see bug #3 - the game feedback continues to report that the target is out of range.
Bug #4 can, with patience, be observed in the unguarded marble spawn just to the west of the eastern outpost on the north side of the road. From time to time a mob, usually a yew treant or a forest oastic, will enter the marble field. The mob can be targeted but cannot be damaged, nor does it attack.
Hopefully the above information, perhaps supplemented in this thread by the observations of other players of these and possibly related bugs, will allow the smashing of these and related bugs
Knossos