What the..... Sea Routes

[OGGleep]

I am having issues with sea routes. I must be missing something, I hope you all can help clear this up.

I am playing as Russia.

The first and only Merchant port I built was in Kursk, midway through the first era. I built a merchant vessel and when I selected it, two ports were highlighted. One in Egypt, and another in Venice. I selected the Egypt one and established the route, I assume this was possible because I also owned Greece and its port of Athens.

Anyhow, I am midway through the 2nd era and decided to continue to make sea routes now that I had some breathing room.

I did exactly what I did before, I made a merchent vessel in Kursk and when it launced I selected it. This time no ports were highlighted. Confused, I built a merchant port in Athens, as this was the direct link to the Venice port. I built a merchant vessel in Greece, and when it Launced I selected it. Again, nothing became highlighted.

What is going on here? No changes in Ownership have happened in between the first and 2nd time I built trade ships. Now I have 2 useless merchant vessels. Can they ever be used to establish trade routes?

Does anyone know why I could establish trade routes to 2 ports with the 1st Merchant ship, but with the 2nd merchant ship, I could no longer select the port in venice?