[Pharo-project] MessageNotUnderstood: UndefinedObject>>includes:

I have this kind of error which appear randomly when I am instantiating and displaying in real world a Morph. Next from the morph is deduced Form field to use as the basis of a PNG image for Seaside canvas. It is easy to fix (or a least prevent the error) but it is system land... so I am curious to read if other meet this problem. See debuglog -- http://blog.ofset.org/hilaire