Why can't I create a test harness on a subsystem in a reference subsystem?

I can create a Simuilnk Test harness on a subsystem in a model, which is fantastic. However, I cannot create a test harness on a subsystem inside a reference subsystem. Why not?

Answer 1

[Mark McBroom]

Try opening the reference subsystem model directly. You should be able to then create a test harness on a subsystem inside that model.

[Todd]

I had tried this. You cannot. It seems like you should be able to.