I am not sure how it changes what I said.
You said "A cargo ship cannot store cargo. But it is not a bug, it is a limitation."
The mustang can store and transport cargo without problem. You go to the terminal, you fill your cargo with stuff you bought, fly on another planet and sell the content of your cargo.
What you can't do is get a package of a deliver mission and put it in your ship because you don't have space to drop it (in spite of that, you can still "cheat" with a tractor beam gun and put the package behind the seat).
Manual packages are not cargo.