On a Mac, when closing one or more PDFs with changes, the "Do you want to save the changes…" modal window should become active, allowing a user to use a keyboard shortcut to respond Save, Don't Save, or Cancel. As it is currently, the user must click the window to make it active and only then can they choose a response.

In other words, this window is modal in that it requires a user response, but non-compliant in that it does not make itself active to provide the response.

This bug is new to Acrobat, but not sure if it is only in the most recent version.