Cannot insert horizontal frame from another frame using palette
If you select a frame then click one of the frame icons in the palette, it inserts the specified frame before the selected frame. Unless you click the horizontal frame icon, then nothing happens. I might guess that with a vertical frame selected it might be wanting to insert the horizontal frame within the vertical, but that doesn't seem to happen either. Basically, nothing happens regardless of what type of frame you have selected. You need to use the menu to insert horizontal frames before other frames.