Docking panes not laid out correctly

We're trying to layout a component that allows for up to 12 docking panes (usually less) set up in a 3 X 4 grid.  We add the docking panes in order from top to bottom, left to right.  This works for a most of the variety of layouts that we've come up with, but there are a few where this doesn't work.

Desired layout of panes:

A	D
B
C

So in this case pane A is created and docked right of the frame itself, pane B created and docked below pane A, pane C created and docked below pane B, and pane D created and docked right of pane A.  We send a CRect into CreatePane indicating that D should be twice as tall as A, but we end up with the following layout of panes instead:

A	D
B
C

Is there a way to indicate that D should be right of both A and B, or another way to correct this so that D is twice as tall but the same width as A and B?

Changing the code to layout the panes from left to right, top to bottom, instead of top to bottom left to right, fixed the layout described above but does not work for other types of layouts.  These layouts can be configured by the user, so I can't give an example of every type of layout, but here's an example layout that no longer works:

Layout by preferences:

A	B	C
D

Layout displayed:

A	B	C
D

So is there a way to indicate a pane should be docked next to two panes, or will we need to find a different way to programatically layout the panes other than top to bottom, left to right or left to right, top to bottom?

We're working on the algorithm to get the panes laid out correctly, but we've run into a layout that we can't determine the correct order of addition: