I was doing a relief effort mission in the Epsilon Hydri K962-Gamma within the Arucanis Arm. I was asked to deliver 10 provisions to the planet within that system. I delivered them the provisions but found I had only delivered 5. I had to go out and purchase more from a cargohold ship in the Sirius Block and purchased 15 expecting to have 10 left when I delivered the final 5 out of 10 that was requested. When I delivered the 5 they instead took 10 leaving me with 5, Ignoring the fact that I had just recently gave them 5. Why is that? Is it a bug or something I should expect every time I do these types of missions? If I chose "Not Now" and went and got the amount they asked for (leaving the system) could I return and give it to them or is it one of those "you got to have it at the right time, right place" sort of deals?
Actually it's a typo / poor description. It says you've "delivered" x amount, but what it really is showing is how many you have available to give them.
The mission will only take the commodity when you have all of the asked for amount available.
Edit to add: the Relief missions will also count commodities in your bank, so if the totals don't match check to many you have in your bank as well as in your inventory.