Before you read this, this is not a whine thread, just an informative thread in which I would like some information on things

I have played a few games against certain British players that tend to use the British Tactical Support Regiment commander. And they always pop the Artillery Cover ability, which costs 250 munitions, before they assault a position of mine that has a combination of tanks or tank destroyers and infantry.
Can someone please explain to me what the Vehicle disabling artillery from this ability actually does? If it hits, it insta stuns your tank, which is fine, but more often than not it will give you a damaged engine and insta stun you at the same time. Now I am just wondering, is this what it is supposed to do?
To me it seems like an ability that always pays itself back. I have situations where one or two Jagdpanzer IVs were defending an area, an area that had seen heavy battle many times. One was more to the front, the other more to the back, so they can cover each other. Then the Brit player pops Artillery Cover and both my tanks get insta stunned and sometimes this comes with a first hit engine crit as well. 99% of the time, my tanks will get circle strafed to death, since Jagdpanzer IVs can't turn that well and the Artillery Cover ability also provides anti infantry artillery, so my volks couldn't fully support my tanks.
Now this isn't a disaster, I have won many games whilst having to endure this ability, I don't find it OP or overperforming in any way shape or form!
So again, just wondering, is it supposed to insta stun and possibly also engine damage at the same time? In other words working as intended or not?
Regards
Current knowledge: first hit insta stuns, second shell always hits due to first shell stunning and engine crits the tank. Can't insta stun and insta engine crit at the same time!
Also thanks to elchino7:
This is Relics changelog
Artillery cover:
Added a delay and warning smoke to give players a chance to react to the ability. Change the stun critical with a weapon disable to prevent constant stun.
Added warning smoke
Added 4 second delay
Vehicle Stun Critical removed from penetration table replaced with Main Gun Loader Injured
What it seems they really did:
Kubelecer:
"it seems like you are completely right. The patchnotes said that they replaced the stun effect with injured loader, which in reality is main weapon disable, but I didn't realize it could damage engines before. Sorry for the previous post.
The shells have 60 damage and 1000 pen, 66% weapon disable and 33% regular engine damage. They drop warning flares and start droppping after 4 seconds. I am not sure but from watching hans once I think the brit needs vision on enemy tanks to make them drop".