A Blueprint that references a macro from a macro library cannot be saved if the macro is deleted and then the deletion is undone

A Blueprint that references a macro from a macro library cannot be saved if the macro is deleted and then the deletion is undone. The following error is given:

Can't save ../../../../../../UnrealEngine/Test/Content/Test/NewBlueprint.uasset: Graph is linked to private object(s) in an external package.
External Object(s):
NewMacro_0

Reproduced in 4.8.3 binary, 4.9.0 binary, and Main (CL 2684415)

1. Open a new blank project
2. Create a new Blueprint Macro Library
3. Save
4. Create a new Actor Blueprint
5. In the Event Graph, reference the new macro from the macro library
6. Compile/Save
7. In the macro library, delete the macro
8. Undo
9. Save
10. Save the Actor Blueprint

Result:
The Actor BP cannot be saved, giving this error:
Graph is linked to private object(s) in an external package.External Object(s):NewMacro_0