Possible to use later developmental course to distinguish alternative hypotheses about earlier underlying representations. If there is a rule at all in this case, it is a rule relating the adult form the child's underlying lexical representations. Macken uses this kind of example as evidence against a self-organization in phonological development. But she seems to have an odd view of what self-organization is, limiting it as phonetic differentiation. From the gestural recombination view of correspondence relation, what child is doing here is extending a novel correspondence relation to new contexts.
Coronal consonants assimilate to non-coronals.
Release from harmony begins first for coronals that follow non-coronals. However, due to incomplete maturation in the intergestural coordination, the constrictions end up being produced concurrently at the beginning of the word. As the jaw raises for the initial coronal, the lips may constrict, even though the UL and LL have not reached their fully displacement from teeth and jaw. Effect will be particularly pronounced in initial position, because the jaw is raised highest at the beginning of a word. High jaw plus partial displacement of UL and LL from their neutral positions will result in a lip constriction, in addition to a tongue tip constriction at the beginning of the word.