I don't know  if this really is a bug or intentional.  But if I right click a target I'll attack it while it is in range, and then when it moves out of my range sometimes my guy follows and sometimes he doesn't.  Also everynow and again he'll only shoot one shot even if neither player moved and then just stand there until I order another command.  Its really annoying if you are chasing someone with a ranged hero.

If I took a guess it has a lot to do with the fog of war.  I notice if I play Reg and get his tracking bug, auto attacking works a lot better.  Maybe for a split second the game is covering the character in a fog of war even though it shouldn't so you automatically stop attacking the char even though he stayed in range.

-BlueFire