Problem with inverted role in African Wildlife example

[chun...@gmail.com]

(1) The example contains the following statement:

Every lion eats an impala.
(2) It also defines this inverted role:
X eats Y if-and-only-if Y is-eaten-by X.

Given (1) and (2) I would expect that the answer to the question "Who-Or-What is-eaten-by a lion ?" should include "impala", but this is not the case. 
Is this a bug or am I missing something?