IMO, Window B should always scroll and Window A never. And I wouldn't change the focus of the window after a scroll.

The two main reasons are:

• Many users do not have the complete understanding of what an active window means.
• Users expect a reaction from the window behind the cursor.

And this is getting more and more true with the significant use of smartphone/tablet operating systems in which the concept of plural windows disappears completely.

By the way, it is the case on OSX since Snow Leopard. (maybe even before)

Here is an example of what I do a lot on my computer:

• I work on (1)
• I have my cursor on (2) and whenever I need an info in that page, I don't have to change the focus, just scroll and continue to type (typing will happen in (1) whereas scrolling will happen in (2))

IMO, Window B should always scroll (but not get the focus if not already in focus) and Window A never.

The two main reasons are:

• Many users do not have the complete understanding of what an active window means.
• Users expect a reaction from the window behind the cursor.

And this is getting more and more true with the significant use of smartphone/tablet operating systems in which the concept of plural windows disappears completely.

By the way, it is the case on OSX since Snow Leopard. (maybe even before)

Here is an example of what I do a lot on my computer:

• I work on (1)
• I have my cursor on (2) and whenever I need an info in that page, I don't have to change the focus, just scroll and continue to type (typing will happen in (1) whereas scrolling will happen in (2))

IMO, Control B should always scroll and Control A never.

The two main reasons are:

• Many users do not have the complete understanding of what an active window means.
• Users expect a reaction from the window behind the cursor.

And this is getting more and more true with the significant use of smartphone/tablet operating systems in which the concept of plural windows disappears completely.

By the way, it is the case on OSX since Snow Leopard. (maybe even before)

IMO, Window B should always scroll and Window A never. And I wouldn't change the focus of the window after a scroll.

The two main reasons are:

• Many users do not have the complete understanding of what an active window means.
• Users expect a reaction from the window behind the cursor.

And this is getting more and more true with the significant use of smartphone/tablet operating systems in which the concept of plural windows disappears completely.

By the way, it is the case on OSX since Snow Leopard. (maybe even before)

Here is an example of what I do a lot on my computer:

• I work on (1)
• I have my cursor on (2) and whenever I need an info in that page, I don't have to change the focus, just scroll and continue to type (typing will happen in (1) whereas scrolling will happen in (2))