Excel scrolls the wrong window on hover

If two (or more) instances of Excel are open, and one of them has the focus, when hovering the second one, scrolling is still applied to the first one. We need to steal focus from the first window of Excel and then scroll the second.

This seems like a bug and can be reproduced easily (more easily with two monitors).

Lets say you have two windows of Excel open : A and B.

You're working on A but you need to read B. hover your mouse over Excel B, scroll... the scrolling occurs in A ! You must click on B, scroll, then return on A.

Now, with focus on A, open another application (let's say Word), and, of course, set the focus to the newly open app. Be sure to see Excel A and B. Hover your mouse over B, scroll... Scrolling still happens on A.

This does not happen with Word or Outlook. If you open 2 windows of Word, the scroll occurs in the one that is hovered, as expected.

I don't think there's a solution, this is a bug and should be adressed by Microsoft.