Yes, that because this is cold blood C++ compiled to machine code, if you call function in C++, CPU unconditionally jump to that function code, UE4 don’t have any chance to detect that and intercept that to execute blueprint implementation of interface, or else engine will generate function definition with code calling blueprint function on compile time, which it does not due as it would needlessly complicate use of interface in C++ (but it does that with BlueprintNativeEvent), insted you call generated Execute_ function which checks if there blueprint implementation and executes it if it is or goes call C++ function if it’s not.