I have the Mac/McDonald nightmare, squared.
My great grandparents were both Mac/McDonalds before they married.

Angus McDonald married Flora Belle McDonald and they seem to flip-flop between the Mac & Mc.

I was going crazy trying to find the family on the Canadian censuses and finally resorted to a visual search.
On the 1891 census I found the Mc/Mac names recorded as "Donald Mc, Flora". The prefix was listed after the root name!
Flora McDonald was Donald Mc, Flora
Angus McInnis was Innis Mc, Angus

That is the stuff that will drive you nuts.
Here is a blog entry on the topic, if interested...
http://epluribus.me/2011/08/14/nova-scotian-nightmare-those-...