I'm not sure how your able to check that they have traded with others or not
In the diplomatic overview you can see (by clicking on their planet) with whom they are trading (the yellow lines).
Let say, you are playing the Terrans, you click in the diplomatic overview on the Drengin planet and you see that they are trading with the Alterians. So now trade with the Drengin and you can see that they want the Universal Translator. Now trade with the Altarians and if they also want the Universal Translator, then you know something screwy is going on.
However to be honest, if myself have not see this recently. Last time i did see it was around the first week of April. And that i remember because i wanted to ask Paul about it in the dev stream (the first one that Kristin moderated).