By Julian Smart.
I found that if I added all non-fixed bars, bars would overlap. This seems to be because the proportional resizing doesn't work before the window is laid out. I worked around this by setting pane sizes before the bars are added:
wxSize sz = GetClientSize();
// Set width for panes to help it do the calculations
int i;
for (i = 0; i < 2; i++)
{
cbDockPane& pane = * (m_frameLayout->GetPane(i));
pane.SetPaneWidth(sz.x);
}