Just discovered a bug in the new release of Photoshop. It's been well documented, but I hadn't known about it before. If you open Lightroom without opening Photoshop, select an image, and choose edit in Photoshop, photoshop will open with the image in it. However, if you add layers, the context menu of the layers will be entirely grayed out.
The work-around is simple: open Photoshop manually before sending an image from LR to photoshop.