That's odd - if you move the cursor inside it I would think you would be able to capture them.
One advanced thing you can try is the 4th option shown in the dialog after you use red box to capture an object/window, which is labeled "Capture Multiple Images, One for teach Child Control".
Use redbox to select the entire window and then choose that..
Either you will be wonderfully surprised that it captures every single control automatically, or you can let me know if it fails.