To reproduce, have two windows open.  Focus one of the windows.  Move the mouse over the other window, and move that window by holding alt and dragging with the mouse.

My expectation is that the window will be focused, but it is not.  I'm using focus follows mouse with a delayed raise, so I find it confusing that even though my mouse is over the window for an extended period of time, the window is not raised.

This also happens with click to focus.  I suppose it can be interpreted that the click is not making it through to the window so it shouldn't be raised in that case, but it feels to me that the window is being interacted with, and ought to receive focus at that point.  As a supporting point, clicking on the titlebar to move *does* raise the window, so the current behavior seems to special-case the alt-pointer method of moving windows.