Detecting dual/horizontal GUI changes

Hi! o)

When switching between dual-h and dual-v I try to make a toolbar switch its position automatically by detecting a GUI change with OnListerUIChange(), because if you make use of a toolbar which sits right between the file displays in dual-h, this toolbar is going to switch from horizontal position into vertical and does not fit there very well. So I wanted to hook in and re-place the toolbars position by script.

Horizontal (before switching dual-h to dual-v):

Vertical (after switching, the green area is where I want any toolbar to be placed, if it was between listers in dual-h):

But.. the OnListerUIChange() event does not trigger if you switch between dual-h and dual-v. It also does not trigger if the viewerpane is switched from vertical to horizontal display.
To make the list complete, it also does not fire for a toolbar I close or open, maybe you find these situations worth to be supported one day. Before I forget, I also had the idea to close viewerpane and any panel open, when demaximizing a lister or when resizing it to be very small. But OnListerUIChange() or OnDisplayModeChange() also not feel like kicking in. o)

Thanks! o)