A service function tries to return Collection<double[]> Aegis throws up its hands and treats this as a collection of anyType. Which, on the read side, tries to run the code to return DOM fragments. However, that reading code is expecting a wrapper element, which, not being there, results in complete chaos.
The immediate fix here is to make this show up as a collection of collections of doubles, not a collection of anyType. I guess I'll try to remember to make another test case for the legitimate anyType array case after I fix the immediate problem.
