Those entries I've checked (mainly Andreas) even when the PR gave the child the father's name (as was custom in Manx ) the IGI has deiberately adopted the English style of using the mother's name.
Posthumous children have father's name if the couple were married.
Some early registers give only the fathers name but you will find several entries in which the mother's name is given and then followed shortly by her burial (I suspect not a death in childbirth - normally the child would die as well, but a later death due to post paturation infection).