Sounds like a bug to me. You do have the ability to look at your commodities while flying in space. You can then hit the Trade Route button to see a list of prices on all the stations you have visited.

So, if you are unable to see them and then land and they are magically there, that sounds like a bug to me.

Hmmm...I will have to try again. I tried my hand at being a bit of a pirate, by blowing up a cargo ship and beaming in its cargo (didn't get much of it), and nearly getting killed in the process after hordes of ships converged on me in retaliation. I barely made it thru the jump gate in time! When I went back to that area later on, I was pretty much instantly destroyed by like 10 or more ships. I guess they have a good memory!

Not everything you tractor in from space goes to Cargo hold. Guns are stored on the guns/missile list, other components on their respective lists. Only cargo goes to the cargo hold. You sure it was Cargo and not a thruster or bots/batteries?

I scanned the cargo of the cargo ship before I attacked it. It had food and water in it. After I destroyed it and tractored in the cargo, then escaped, it didn't show up in my cargo hold under commodities while in space, but it did once I landed and was at a commodities dealer.

Are you using a hacked save? This happens in my hacked saves... I've found alot of the things I tractor in don't show up when I check my hold...