Nothing seals perfectly, and the thinner the tube and the higher the pressure, the quicker air will leak out. That's why race teams inflate their tires with nitrogen - not (as some will tell you) because of temperature issues, but rather because nitrogen molecules are larger than oxygen and other gases in air, so it leaks out more slowly.

I usually lose 10 psi overnight from my 700x23 tires with inexpensive tubes.

On the other hand, CO2 molecules are smaller than either oxygen or nitrogen, so when you inflate a tube with a CO2 inflater, it will go flat much more quickly than usual. Some people actually let all the air out of a tire once they get home after they've inflated it with CO2, and re-inflate it with room air.

Your other bikes lost air too, just apparently more slowly with the heavier tubes and lower starting pressure.