If you pay money for supplies and repairs such that the CIU's caps exceed 65535 [Hint: 2^16-1 - maximum value of 16 bits - short int in 'C'/'C++'] you can not later sell equipment and scrounged junk to the CIU to get your all your caps back. The CIU will return caps in exchange for goods until it falls to 65535. After that you can continue selling it things and it will tell you it is going to give you caps for them, but it doesn't.