Hi Henk!
I haven't replied for a while because I have been sitting and working on the plugin.
The main problem was the overload. It was screwing up stuff. It took a while to find.
Another problem is the awkward API here, which I think needs to be changed. It's an object but not an object. It has overloading but registers keywords. It has a few mutable options and some places in which they are immutable.
Because it's still not 100% working (because of this API I don't have the time to wrangle into proper behavior), I haven't submitted a pull request for all the fixes so far.
I'm willing to rework the API and make it consistent, resolving the issues and providing a full pull request, but I won't do it unless I know you're okay with it.