With CDR alt-tab switching and focus-follows-mouse, it isn't always
possible to navigate to all windows.
Example: make three windows, such that they all partially overlap each
other. Then, for each pair of windows, place the mouse cursor on the
overlap between those two (but not the overlap of all three), and use
alt-tab to switch between the windows.
You will find that where a window switch gives focus to one window and
also raises another which the mouse happens to be over, focus is grabbed
from the intended window and given to the raised window instead.
I hope I've explained this clearly enough..
It's fixed in current release