Native default subobjects nulled in child Blueprints on compile

From reporting UDN:

"We had a weird issue with new components added in C++ not being instanced properly on non-direct Blueprint children.

It seems to happen if loading of the parent BP is deferred. It might be related to the code inside USE_CIRCULAR_DEPENDENCY_LOAD_DEFERRING not instancing components in case of deferred loading."

1.) Create a new (blank) C++ project

2.) Save the level and setup as startup level

3.) Add a new C++ class to the project based on ACharacter, (AMyCharacter)

4.) Add an ActorComponent (e.g. a capsule) to the character in C++ just for reference (this one will behave correctly)

5.) Start the engine, create a blueprint based on MyCharacter (BP_MyCharacterBase)

6.) Create a BP based on BP_MyCharacterBase (BP_MyCharacterChild)

7.) Open BP_MyCharacterBase, add a variable of type BP_MyCharacterChild to the BP (so the parent references the child)

8.) Place an instance of BP_MyCharacterBase on the (startup) level

9.) Save everything, close the editor 

10.) Add a new capsule component to AMyCharacter in C++ 

11.) Start the engine 

Observe the following:

• Check BP_MyCharacterChild with property editor. The newly added component will be in the transient package

 

CapsuleComponent'/Game/BP_MyCharacterChild.Default__BP_MyCharacterChild_C:ComponentTest_Good'

CapsuleComponent'/Engine/Transient.Default__BP_MyCharacterBase_C:ComonentTest_Bad'

 

• If you open BP_MyCharacterChild and hit Compile, the component will become nullptr (and it will have an empty details panel)