Humm... When using mmaps, stun the target just after use the spell could be a problem. But this is related with MaNGOS, isn't it?
Anyway, on retail, imagine that you charge and you must follow a large path. I supose that, if the target moves when you are charging, the position of the target is updated and you will finish the charge at target's real position, not at the target's initial position, and apply the stun in that moment. Or I'm wrong?
Not sure if it happens in all cases but if warrior doesnt reach target on charge he will NOT stun target (target blinking directly after warrior start charging will make him 'avoid' stun)
and yes instant charge stun is normal bug becouse in DBC its trigger-effect therfore is always casted on charge cast