The two factions that start with units on trade spots have mixed fleets, the only logical reason the dev's would do that would be to provide fleet protection, which leads to the conclusion that trade spots were/are meant to be being raided. That they are not looks like a pretty obvious issue, bug may be too strong.

There are some other fleet problems that are probably considered more pressing, but trade spots attacks, and a tweaked fleet generation system that considered increasing faction wealth where a trade spot has been captured would be quite a major game improvement.