Using a custom #define as the condition for a UFUNCTION's declaration will cause the function to not show in blueprints

Using a custom #define as the coniditon for an #if / #endif that encapsulates a UFUNCTION that is marked as BlueprintCallable will prevent it from being visible in blueprints despite the #if resolving as true.

This does not occur if using already define specifiers, such as WITH_EDITOR

1. Create a new blank C++ project
2. Create a new C++ class based off Actor called MyActor
3. In the .h file, add the following line at line #7

    #define WITH_CUSTOM_DEFINE 1 

4. In the same file, add the following lines at line #23, under the Tick function's defintion

   #if WITH_CUSTOM_DEFINE
   	UFUNCTION(BlueprintCallable, Category = "MyFunction")
   	void TheFunction();
   #endif
   

5. In the .cpp file, add the following lines at line #29, or below everything else

   void AMyActor::TheFunction()
   {}
   

6. Compile the project (ctrl+shift+B)
7. Create a blueprint based off MyActor
8. In the event graph, right-click and type in "The Function"
   Result: The function doesn't appear
   Expected: The function should appear in this list