Hi Eric,
Did you want the third one into one of the first two?
Resulting in thisform.container1.container1 ?
It may look as if you did so, but I assume the third container is still on the form level. It's only visually within the boundaries of a container.
You need to activate a container (use the context menu/right click - "edit") and then can put a container into it. You'll see the outer container will then clip the inner container.
For faster selection use [CTRL] key with a normal left click to activate a container. You can click through many levels faster that way.
Bye, Olaf.