During a research in the Municipal Archive at Doorn, today accomodated at Wijk bij Duurstede at the "Regionaal Historisch Centrum Zuidoost Utrecht", some more clarity about the origin of the surname ABERNAU came across. On Werner Abernau's Dutch personal registration card, which is in this archive, the following note was literally taken down - inclusive the typing errors:
"Ing macht van den Min v Just van Pruisen dd 22 Oct 24 feslachtsnaam "Abramczyk" gewijzigd in Abernau".
According the arhivist of this archive at Wijk bij Duurstede, this mention must have been copied from a statement in writing, which Abernau at that time could present, or from his passport which he had too. So it has been appeared that in 1924, when he was 23 years of age, he has changed his name because a): he was no child of Abramczyk or b): he would like to start a business.
Source: a visitor of the website (Mrs. Anneloes Smits) and the Regionaal Historisch Centrum Zuidoost Utrecht in Wijk bij Duurstede, www.rhczuidoostutrecht.nl.