Arrow next to folder missing

The root of my data drive has 4 folders, and none of them have arrows (when pressed expand the folder contents).

See the screenshot:

(in case the image doesn't show - here's a link:IMAGE It's strange - I see the image when editing the message, but not when viewing the finished message!)

If I double click on the folder, I see the sub folders and files. But why can't I see the arrow?

The drive is the 2nd Apple GUID partition of my internal mac HD.

I'm on ML 10.8.3