When you pull Aidonium, and then click "sell all", your cargo sees it as losing 0.1 space, rather than sell all. For example:
Cargo space: 100/150. (20 Aidonium).
Sell all.
Cargo space: 98/150.

It still treats it as gaining 5 space, but the text is wrong.

Yeah, it does something like this when you collect minerals too--after you collect minerals click the "Trade" tab before you sell them, you'll see that your cargo space is actually overfilled.

yep... a long-standing and yet pretty simple bug to fix...
probably been marked down as very low priority
it's actually a shame to see such a minor bug in such a nice game