Wings have N/A fuel by default

1. Drag a new wing into the designer.
2. Open the new wing's part properties.
3. Notice how the wing contains 0 kg of fuel despite the fuel capacity slider being maxed out. The performance analyzer shows N/A fuel capacity.
4. Changing fuel capacity or resizing the wing seems to fix the issue.

A question: Fins seem to be unable to contain fuel. Is that intended? They also seem to have a different "density" compared to normal wings. 100 vs 200, in fact.