Hello Heiggwinie,
for the destroyer this is a bug : as I removed the ability to transport scouts (because this feature was not working anymore but gave some trouble) I forgot to remove the CargoI promotion of the destroyer.
As it seems this gave it the ability to transport planes which was not intented!
Later this evening I will release version 4.1 to correct this bug and remove the instal heal (as it should be).
Unfortunately ver 4.1 will not be compatible with saved games from ver4
(just crashed my current game!)
Are these two aluminum suppose to release or is the only way to get them back is to finish building the Aircraft Factory and then sell it?
From a practical point of view you should get the resource back. But interrupting the production may break/bug something in the game mechanics, making it unable to give you the resource back.
So the safest way would be to finish the building and then sell it. If it's so then it's probably the case with units as well!
I had the same kind of problem with a mine on an iron deposit :
I stopped building the mine to put a citadell, which should have connected the iron to my empire as well. But I never get the iron, even when I destroyed the citadell to try with a mine.