Ironically, this may have gone unnoticed if scrolling and zooming behaved in standard ways since I wouldn't be attempting to pan the image with. You would be hitting Undo as I must frequently do in BC due to an unintentionally offset image. Imagine a program which allows you to in the left pane to select text but doing so in the right pane deletes the text instead, or converts it to all-caps. Do one or the other, not both (or better, select a zoom region instead). The two behaviors are inconsistent and it's frustrating. Does anybody even use that feature? On the other hand, on either of the left or right images pans like many other programs. In BC4, on the difference image introduces an offset, which is pretty counter-intuitive and incredibly annoying.
The entire interface feels incredibly constraining. It looks like BC4 doesn't have either option. In BC3, I could use side-by-side or even hide the difference image to increase screen real estate and mitigate the problem by reducing the need to scroll. The zooming mouse wheel in BC4 is even worse than it was in BC3 due to the small display area for images.
This is true in Firefox, Gimp, Inkscape, Libre Office and many other programs. Additionally, many programs use to scroll horizontally. Standard mouse wheel behavior is to scroll vertically, not zoom.
I just upgraded to BC4 (finally) and still find the behavior of the mouse wheel in the Picture Compare window to be very counter-intuitive.
