Discussing on gitter last week it was not clear from the spec how to handle duplicate keys in a received tracestate.

The tests require the tracestate is dropped in such a case:

The example in the spec about going through a system twice is also a bit confusing, https://w3c.github.io/trace-context/#combined-header-value

I think it would make more sense, even though it is an example of what shouldn't be used, to say it shouldn't be congo=congosSecondPosition,rojo=rojosFirstPosition,congo=congosFirstPosition simply because the newer entries should come first.