Well, it's a pretty specialised case, but here goes...
say you've pinned your browser window to your taskbar; with a single monitor setup, when it's not running it shows up just as an icon, and when it's running that's replaced with an icon in a button.
Running DisplayFusion with 'all taskbars show relevant windows', if you shift your browser window to another monitor, then the button-icon will move with it; that's great. Unfortunately, windows treats it as having closed the window - you still have the icon on your main taskbar, and clicking it will open a new browser window. As far as windows is concerned, you don't have a browser window open.
This can be avoided by using 'windows taskbar shows all icons' (or 'all taskbars show all icons, for that matter), but they're not settings I like. It can also be avoided by geeking up, getting rid of the pinned icons, and setting up a bunch of hotkeys instead - which is what I've actually done. GUIs are for lusers, right?
I guess the ideal behavior, from DisplayFusion, would be that if you move a pinned-tab window to another monitor in that sort of situation, that the icon for it displays properly on the correct window, and the 'closed' icon that normally stays in the main taskbar gets hidden somehow, only to reappear if you
actually close the window. I have no idea whether that is feasible from a technical standpoint, though, and as I say, I've hotkeyed my way around it instead.
For the record, I'm loving having the icons on my left hand monitor right-aligned; it makes the glance to find them much less eyeball straining.