How do I rotate items in the Portal 2 Map Creator (DLC, not Hammer)

I've dropped back into Portal 2 as the Map Creator DLC has recently been released. This allows you to create maps (from basic through to advanced) with a number of limitations. However, I cannot, for the life of me, work out how to rotate things.

I have this ramp:

How can I get it to face the exit, rather than looking at the wall? I've tried all manner of keyboard keys and shift-click, ctrl-click.

If you select the ramp, so that it is highlighted in yellow, then you can rotate it by clicking and holding at the bottom of it and moving the mouse. The area you need to click will be shown by a white semi-circle as in this image:

The white semi-circle, or a white diamond, is also used on other rotatable elements in the map editor.