Opening volume views in certain ways makes it so that the 3D content is not visible on the LKG.

[jcfr]

From Albert:

Open Slicer
Use MRHead from the Sample Data module
Go to the "Data" module
Right click on the "Show/hide branch or node" item for MRHead
Select "Show in 3D views as volume rendering"
The scan of the head will show in the 2D display, but will not show in the LKG.