Should be self explanatory...... Look back at the pics on the first page. If you look at the one from the back, the swing arms pivot in 2 different places. Not in the same line..... The drive side pivots farther back than the non drive side. The drive side is also longer, because it's mounted behind the frame,off those 2 bars. The non drive side pivots AT the frame....
I'm not an engineer, but I know this can't be an effective /efficient drive set up/ suspension set up. 3 of your corners are holding up all the weight of your kart, leaving the drive side to do as it does......

I could be wrong, but at this point, there isn't a better explanation. You put a solid bar in place of that shock and it did the same thing..... Because there was still no weight on it. The weight is shifting onto the other 3 axles....
IDK