Can you set a custom theme as the default theme?

I'm trying to make a custom theme the default theme. When I set it as default by right-clicking it from the Themes button and choosing "Set as Default Theme", it "works" for the next blank project I create, and for the next Software Simulation I record. But if I close Captivate and then make a blank project or Software Simulation, not only is the default theme back to Pearl, but the custom theme isn't even listed as a possible theme in the list of themes. What's going on? Any help will be appreciated.