Ok, I've been testing this. Here's exactly how it works on my system using a Dell 4x3 19" monitor at 1024x768. Biab opens up full screen and I can't see the borders of the Biab window in order to grab it to resize. I have to hit the minimum/maximum button in the upper right corner next to the X that is used to close the program. Hitting that min/max button lets me see the borders. Just doing that doesn't effect anything. Biab plays and the screen scrolls fine. I can grab the side with the mouse and move it in to resize the window. Biab still scrolls like it's supposed to BUT, when I grab the edge again and move it either in or out that's when the scrolling stops working and the chord grid overlay happens. Then as Kent said I have to close it and reopen and all is good. I've done this 10 times now and this is exactly how it works.
The reason I have never seen or reported on that is because I have a 4x3 monitor and there's no benefit to try to have more than the main window open so I've never resized Biab before now. I can see that those with large wide screen monitors may very well want to have more then one window visible because they have the screen real estate to do it.
So Eddie, I know you said that closing and reopening Biab doesn't help. Are you absolutely sure about that? Are you saying that after a reboot and you open Biab for the first time you still have the scrolling problem? I'm thinking that the first thing you've been doing is to resize the window then open a song and play it. If that's the case, just let Biab open and don't try to resize, just play something and see what happens. If that works for you then yes, that's a bug but it's not a show stopper. You can get your work done until they can fix this.

Bob

Biab/RB latest build, Win 11 Pro, Ryzen 5 5600 G, 512 Gig SSD, 16 Gigs Ram, Steinberg UR22 MkII, Roland Sonic Cell, Kurzweil PC3, Hammond SK1, Korg PA3XPro, Garritan JABB, Hypercanvas, Sampletank 3, more.