Thanks for making the video! It helps a lot.
It seems like you maybe are accidentally holding down your Ctrl key? (Cmd key on Mac) At least with normal behaviour, you can hold that key down and get easy access to quickly adjust pen size by dragging left/right and opacity by dragging up/down.
While this feature has been a request of several people – it might not be good for everybody. My guess is you are using undo (Ctrl Z) a lot and therefore maybe you are unconsciously keeping your Ctrl key pressed sometimes – even though you are in the middle of drawing lines.
At some point fairly soon we will make the keyboard shortcuts customisable – and then it will be easy to just get rid of this shortcut if it doesn’t fit your way of working.
Let me know if I am guessing correctly 😉