upgraded Nau unable to sell exotic goods

I'm playing as Portugal and once I researched Navigation I upgraded my two Triremes to Naus, but they don't seem to have the sell exotic good button. I see in their list of promotions that it is there, but there is not option for them to use it, not even a grayed out one. My newly built Naus are able to set sail and make me cash as intended but my upgraded ones cannot.

Maybe this is a bug and maybe its supposed to be like this? Its unclear.

They keep the exotic good promotion after you used it; so maybe you already used it?

I for myself did both things: Upgrade triremes into Naus and have them sell goods as well as Naus upgrade to Ironclads which then still were able to sell goods. If you're sure you got a bug here, you should provide a savegame (on the turn before you upgrade them).

Someone else reported that only newly built Naus can actually do the exotic trade trick. Apparently Naus resulting from upgrades get the promotion, but can't do the trade. We'll see whether Firaxis intends that to be the case when they issue the Fall patch.

I suppose I can try to go back and grab a save and post it here. Or maybe I'll try to recreate it and grab the save from there.

But I'm very sure I never used it. Honestly, I wasted a lot of time wandering my Naus around thinking that CIV had a peculiar definition of "adjacent".

I'm not much more than a dabbler in programming, but I can imagine how this sort of thing could be coded wrong with a one use ability.

This was an advanced start game, starting in the middle ages, so maybe that was a contributing factor as well. (I was eager to see how Portugal and its trading capacity played out, without much waiting)