This might be an intended behaviour, but I think it's not.
If there is a factory which produces nothing (or electricity) and comsumes two or more materials, it should be operated only when all the necessary materials are provided, I think. But actually the factory starts operation, even if only one of the necessary materials is provided.
For example, "Heizkraftwerk" in pak.German produces electricity and consumes coal and oil. If one of the energy sources is provided, it starts operation and produces electricity.
I think, that it is intended. It is sufficient for the "Heizkraftwerk" to have one raw material, it didn't need both. The same for a supermarket, which sells meet and fish, e.g.
I think rules for end consumers (nothing produced) are different (as you found). And electricity (iirc) is not a production good per se, but rather byproduct of activity...