I could notice that there is a little error somewhere in a CanReceiveFocus method or MoveActiveCell (SelectionBase):
If a spanned cell is focused and you want to navigate to the left cell with arrow left key (keyboard), it doesn't work. You have to press the key the same amount of times than the ColSpan value.
To avoid problem, the check with CanReceiveFocus should be changed, or the Focus method.
I could sove the problem by adding
newPosition = Grid.PositionToStartPosition(newPosition);
in "MoveActiveCell" method, before the last "if" test (Focus).
But I don't know if there are some other places where the bug could happen.
Note: I made a mistake, the attachments/comments do not refer to this issue and should be removed, what I'm not allowed to do.