So now I've learned that this is a result of the way Pickler is
implemented. I think that it would make sense to create an
implementation that is not that recursive and that would handle such
structures better.
I have now written one such implementation that is a subclass of the
original pickler and handles recursive data structures. I presume that
it is inferior in a couple of ways (performance and memory efficiency
probably), but a complete rewrite could probably create an
implementation that handles recursive data structures and is not inferior.