Texture numbers not the same everywhere

It’s confusing that he first texture slot is numbered 0 in Material IPO’s, but numbered 1 in other places (e.g. particle emission control). Is there a good reason for this? Are they really the same texture slot?

That is confusing, especially since the Particle Physics tab doesn’t have a Material-0. May be just a result of too many people working on it at the same time.