Nanite Assault Beam

I apologise if this has already been covered (although I have looked and can't find much on the subject), but I am confused about how the armour reduction of the Rankulas' Assault swarm should function. On creation, I see that the swarm autocasts its assault beam ability, but even after the ability cooldown is complete, I notice that the swarm attacks still cause armour reduction and the swarm doesn't autocast it again even during combat. Is it necessary to keep pressing the button to keep the ability on (i.e. allow the swarm to reduce armour), or is the button in some way redundant?

Also, at higher levels, the swarm attacks should get increased armour reduction (this is reflected in the mouse-over description), but I have noticed that this doesn't automatically happen. Whatever the level of the ability, the swarm only causes a -2 reduction when it is first created and the upgrade doesn't seem to happen until you physically press the ability button, at which point the armour reduction is then corrected on the next attack. It's a bit counterintuitive to me, since the increased armour reduction is then only available for 120s of the swarm's lifetime, and only if you happen to remember to click the ability button. Is this the intended behaviour? What am I doing incorrectly?

I am currently running the 1.50 Beta, but noticed it in the 1.49 version as well.