Now that I have a copy of A History of Freemasonry in South Carolina: The Years 1860 - 1919, more information concerning Brother Mackey is available. It seems that the effects of the War Between the States were still being felt within the Fraternity in South Carolina (see also: Pushed to the Brink: The Stresses of War on Freemasonry). From the portion of that text that addresses 1866 and the end of Mackey's long service as Grand Secretary in South Carolina, this following footnote is found.
The proceedings of the year 1921, more than 50 years later, indicate that the elections were bitterly divisive in 1866, and that Mackey was rejected because he had sided with the Union supporters during the War Between the States. The collapse of the Confederacy would have brought considerable wrath on the head of one who had spoken out against the Southern cause. What is remarkable is not that Mackey was defeated, but that the proceedings do not explain why until 1921.1Brother Mackey's final years in South Carolina were clouded by suspicions and allegations of financial irregularities in regards to the Grand Secretary's office. A motion - one which was never acted upon - was actually made during the 1868 Grand Communication to expel Mackey from the Order.2
Mackey left South Carolina two years later.
1. Cornwell, Ross & Willis, Samuel M. A History of Freemasonry in South Carolina; The Years 1860 - 1919. The Grand Lodge of Ancient Free Masons of South Carolina, 1979, p. 26.
2. Ibid, p. 35.