I noticed the same thing. If you build trade ports you get boxes to use in the trade window (F8). If you do not allocate them to "boosting" your exports of a particular resource then the boxes seem to stay in the "import" area up the top. However nowhere does it say what importing does for you or what it imports.
As soon as you allocate an import box to an export slot you get trade income showing in the exact amount allocated by the box in the appropriate credit/resource summary.
Essentially if not using the boxes to export goods what are they doing in the import area? Importing what? Do they give you some trade market bonus when "importing/buying" resources?
The other question is one of why putting a box in the "credits export" area then brings in credit income? So is my faction selling credits and somehow making credits from the sale? Apparently exporting metal produces more metal for my faction without any loss due to the export? Same for crystal, trading my crystal via export somehow actually increases my production of crystal via trade ships?
Export credits should = metal or crystal income
Export metal should = credit or crystal income
Export crystal should = credit or metal income
Import credits should = loss of crystal or metal income
Import metal should = loss of credits or crystal
Import crystal should = loss of credits or metal
Another thing this brings into question is when trading with trade posts and ships internally, we are relying on the internal empires economy to generate profit of something during the exchanges as a trade ship arrives at it's destination. So a private deal that concludes between two citizens or companies that upon arrival an agreed amount of money should be exchanges for goods or services. I liked when distance counted as time was then taken into account, but also it would be nice to know what each trade ship was carrying and to where and at what profit of what good?? This would make raiding more interesting. As I understand it at the moment trade is probably a simple top level number that would be reduced by a set percentage each time a trade ship is destroyed?
P.S. Is there a way to physically determine trade routes? I know a major trade lane in sins1 was white?