Subclasses_of - why does it ignore subclasses within modules

ActiveSupport provides a method Object.subclasses_of, to give the
subclasses of a given class. However, it ignores any subclass within
a module, so :

class A
end

class B < A
end

Object.subclasses_of(A) # returns [B]

module C
class D < A
end
end

Object.subclasses_of(A) # returns [B], even though C::smiley: is also a
subclass of A

class E < C::smiley:
end

Object.subclasses_of(A) # returns [B, E], even though C::smiley: isn’t
returned

This behaviour has been very deliberately built into the code, but
seems to be plainly wrong. Can anyone provide any insight why this is
so?

Tom