Editing static functions in Blueprint Function Libraries with hotreload can cause saving issues with blueprints calling them

When editing a Static function from a Blueprint Function Library, any blueprints that have already had it added are unable to be saved. This can be worked around by removing the node and adding it again, but this is not optimal.

Regression?: Yes
Did not occur in 4.12.5 Release (3039270)
Occurs in 4.13.0 Release (3106830)

1. Create a new project
2. File > Add C++ Class > Blueprint Function Library name it MyBlueprintFunctionLibrary
3. In the .h, add the following code on line #16

    public:
   	UFUNCTION(BlueprintCallable, Category = "NotWorking")
   		static void StartBug(); 

4. In the .cpp, add the following code on line #6

    void UMyBlueprintFunctionLibrary::StartBug()
   {
   	UE_LOG(LogTemp, Warning, TEXT("Test:"));
   }

5. Compile the project and return to the editor
6. Create a new blueprint actor
7. In the event graph, have the blueprint call the Start Bug function, compile & save
8. Return to the .cpp and change the TEXT macro to Test2 from Test
9. Compile the project
10. Return to the blueprint and add a print string node (just to make it compile), compile & save
    Result: An error appears saying that the graph is linked to an external package and is unable to save
    Expected: The blueprint should be able to save without an issue