Can't save level (external object) when setting the default static mesh for an instance static mesh component

User cannot save a level containing an actor using a custom instance static mesh component after the default in both the actor and the custom instance static mesh component have both been set.

1. Open the editor
2. Create a new Blueprint derived from Instance static mesh component
3. Create a new actor blueprint
4. Add the new instance static mesh component created above to the new actor blueprint
5. Set the default static mesh for the instance static mesh component that was added to the actor blueprint
6. Add actor to the level
7. Save all
8. Open the Instance static mesh blueprint that was created at the beginning
9. Set the default static mesh
10. Save all
11. Notice that an error is given (see image below)

Expected: The default for the new component would be set to whatever static mesh was used
Result: The level with the actor can no longer be saved