Well I must admit that now it's hard for me to replicate scientifically the problem. I tried several times and sometimes it happens, sometimes it doesn't.
But I managed to create a sample of the "problem" in an empty project. you find it in attachment.
Try to split the first midi item and to move the second half, you should notice the issue in the "Gain-low Shelf" envelope. I recorded it in a gif.
https://drive.google.com/open?id=1D9...5SFB_rQ3S3dirJ
SL