It just doesn't show up in shading at all. I remember reading in one Blender Forum awhile ago, from a developer, that it could be a GPU issue... but it really seems like a bug. Anyway, kind of a bummer.
Jonathan Lampel
replied
That is a bummer! Although you already mentioned it, I'll add this in case someone else stumbles on this looking for help: Matcaps only show up in solid shading view. Occasionally material and texture view can look similar to solid shading, so it's easy to forget to switch over to find the other shading options.
