Not true Jim.
Michael Laffan, head of the School of History in University College Dublin writing in "History Ireland."
http://www.historyireland.com/20th-century-contemporary-history/the-emergence-of-the-two-irelands-1912-25/

"it was agreed that a boundary commission would decide the border between the two parts of Ireland. It is significant that the treaty split centred on questions of sovereignty and the oath of fidelity ('allegiance') to the king rather than on the question of partition.Few Dáil deputies discussed the matter."

That split became the civil war, and it was not about partition.