The best workaround I could find is this. On the PopupContainerControl set AutoSize to True and AutoSizeMode to GrowAndShrink. Then in the ClientSizeChanged event of the top level container control (could be a Panel or the Form itself, doesn't matter) redefine the PopupMinSize of the PopupContainerEdit as follows:
Size popupSize = new Size(popupEditControl.Width, popupContainerControl.Height);
popupEditControl.Properties.PopupFormMinSize = popupSize;
The only problem I've got with this solution is that once the form is increased in size the popup resizes correctly, but when the form size is then decreased the popup container stays the same size as before. We've left this implementation in place because at least it will continue to show the entire contents of the popup whereas before it was cutting off significant portions of the contents of the popup container.
Hope this is useful to you in some way.
Regards.