Mixer Display not scrolling.

For some reason, when I have many channels on a mixer, the mixer stops responding to the scroll bar.

I generally have about 80 channels, vsti +audio. I route those to 8 groups and then the groups to my main stereo outs.

I’ve created three seperate mixers. One mixer with everything, one with the groups and one with the outs. I use each for different stages of mixing.

However, on my main mixer window the scroll at the bottom doesn’t seem to want to do anything. Once I have over a certain amount of channels the scroll bar moves, but the mixer doesn’t seem to respond. Consequently I have to open up a secondary mixer to view my groups.
I’ve checked visibility settings and the Groups,Outputs and FX are checked. I’ve tried changing zones for those things but the effect is still the same, channels on the right don’t show up if I have too many visible.

Is this a bug or a feature that I can turn off.

Here is a link to the video of the problem: