CS Goes down when killing jungle creeps

So, this isn't the only time this has happened (this bug has actually happened to me on multiple occasions) but out of all the times, I actually got video of this bug happening.

As you can see, BRNA is farming. After he kills that final creep wave, he goes up to 277 CS. After he runs over to the krugs, and kills the small krug, his cs goes from 277 to 275.

Over the multiple times I've seen this there doesn't seem to be a certain number that the cs goes down by, it just seems to be really inconsistent, like I've seen it drop by around 20 once and sometimes it only drops by a few cs, like in this case it only drops down by 2.

I know that this doesn't actually have any super major effect on gameplay, but it does help to know how much cs you've acquired throughout the game, accurately, especially if you're someone in low elo like me who is still working on their farming skills in hopes of becoming better.

Thanksssssss:)