Find_with_ferret :multi not working for me (latest version)

Previously, for all my ferret searches, i was using find_by_contents,
like this:

@stuff = LearningObject.find_by_contents(“trumpet”,
#ferret options
{:multi => [TeachingObject, LearningObject, Lesson, Course],
:page => 1,
:per_page => 15 },
#find options
{} )

That all worked fine. We’ve upgraded to the latest ferret/a_a_f,
though, which no longer uses find_by_contents: i believe we’re supposed
to use find_with_ferret instead. However, if i do the equivalent, with
find_by_contents replaced with find_with_ferret, then the ‘multi’ part
doesn’t work: i get the same results as if i didn’t pass multi at all.

My ferret-indexed classes all have “:store_class_name => true”, which i
read was necessary for multi searches. Can anyone help please?

thanks
max