Why can't BlueprintImplementableEvent in interface can't be const

Development Programming & Scripting UI
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1

I had a couple of methods declared in an actor class as follows:

UFUNCTION(BlueprintImplementableEvent, BlueprintCallable, Category = Setup)
FVector GetBoatForwardVector() const;

This worked and could be implemented in a derived BP.

However, when I moved this method into an interface, it would not compile :

UINTERFACE()
class UBuoyantObjectInterface : public UInterface
{
    GENERATED_UINTERFACE_BODY()
};

class IBuoyantObjectInterface
{
    GENERATED_IINTERFACE_BODY()

    UFUNCTION(BlueprintImplementableEvent, BlueprintCallable, Category = Setup)
    FVector GetBoatForwardVector() const;
};

It causes the following error:

cannot convert 'this' pointer from 'const UObject' to 'UObject &'

This is resolved by removing the const specifier on the method. How can I keep the const specifier and have this method declared in the interface?