Is manumission allegiance established upon the children if the father's lineage is unknown and the mother is a freed slave?

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If the father's lineage is unknown and the mother is a freed slave, allegiance is established upon the children for the mother's master, according to the opinion attributed to Abu Hanifa, Muhammad, and Ahmad, and considered the apparent view of Al-Shafi'i by Ibn Al-Labban. The reasoning is that the cause for establishing Walaa for the mother's master is present, and the impediment (the father's freedom) is only assumed in the agreed-upon case where the father is known to be free. When the father's freedom is not known, doubt exists regarding the impediment, so the ruling remains upon the original state, and the established cause should not be abandoned due to doubt about the impediment. However, the established ruling is that the father's freedom is presumed; therefore, allegiance should not be negated based on mere speculation regarding the child's status. Furthermore, the cause for establishing Walaa to the mother's master requires the father's servitude, which is absent in presumption and appearance.