Explain/1,2 seemingly not working with "include"

explain/1,2 can be quite useful, but while testing some predicates (for which I knew there existed multiple instances) I found some seemingly odd behavior regarding include, namely:

  • “include” won’t report the existence of include/1 and include/3 (there are also DCG rules, again not reported);
  • “include/1” won’t report the predicate (as per above);
  • “include/3” reports the predicate but won’t give further info about it (definition file or references).
?- explain(include).
% include is an atom

?- explain(include/1).

?- explain(include/3).
% include/3 is a predicate

Is this expected behavior and if so, why?