Years ago, in Dog World magazine was a article in mixed breeds becoming "designer". It started the process of being a recognized breed as generations of the same producing the same in appearance, color = equal to a standard.
In this article was a comparision to this use of names- the example was a Pekinese and Poodle- producing slang "peekapoo". However A peekapoo is out of these two breeds. There for when the off spring a peekapoo to peekapoo, as no longer were the parents a Pekinese and a Poodle- but pekapoo to pekapoo- thus making a tongue in cheek joke of a " peekpeekpoopoo.. Their point was all the others breeds bred originally from two different breeds became a seperate identity- and these designer ( mutts) can not. Their final point was, If a peekapoo became a real peekapoo, then it must at least 3 generations to establish the breed will maintain its looks in appearance etc.
Its like that old joke- what the breed comes - when a Bull Terrier is bred to a Shitzu- it becomes a bull---- ( fill in the blanks. but you get it..)