Chaffey & Chaffin families — the same?

My great-great-grandmother Catherine Harris married twice – first to Thomas Cheafey or Chaffey, and second to James Andrew Hayes. She had a son by her first marriage, Charles Thomas Chaffey, who apparently changed his name to Chaffin. I wondered why he might have done that, and then someone drew my attention to this:

http://genforum.genealogy.com/chaffee/messages/505.html

which describes someone else doing something similar.

When it happens one, it is odd. When it happens twice it begins to look like a conspiracy!