There seems to be an issue with placing a portlet on a page with multiple layouts.
Create a page and add a one column layout - followed by a two column layout. Click the add portlet + button on the second two column layout. Select a portlet in the selector. When it returns back to the page - the portlet is always added to the top layout. You than have to edit the page.psml file and move the fragment into the appropriate place.
If you use the arrows - it places the portlet in the layout - but it does not resize to the columns. Once again - you have to edit the page.psml file to place it in the right place.