There seem to be a couple issues with the IS BASE check box and subsequent list boxes:

1. May selections (such as Set | Prop) do not allow the IS BASE check box to be checked. Yet, may set props could be bases. For example, a car prop could be a base for different paint jobs.
2. When IS BASE is available, it requires a category selection and a sub-selection. The category selection has options such as G5 Character, G3 Character, Non Standard Human, etc. It includes selection of Prop and Accessories. However, these selections are absolutely useless because neither Prop nor Accessories produces any options in the sub-selection but the Store Manager will not save the page unless as sub-selection is made.

"We often compare ourselves to the U.S. and often they come out the best, but they only have the right to bear arms while we have the right to bare breasts"
Bowser and Blue, Busting The Breast