Incidentally, the same is true with “hardcover” and “hardback” – I use those interchangeably, but was recently corrected when I said “hardback.” I was told that “paperback” is okay, but “hardcover” is preferred and “hardback” is incorrect.

And there’s an interesting discussion here about the mast/staff vocabulary issue: http://www.cbc.ca/news/indepth/words/flagflap.html – it’s from a Canadian perspective, but also gives background history and includes American information too.

I did want to mention one picky detail, which is the use of the phrase “half mast”. Many people incorrectly use this phrase to describe flag position on a pole on land. The correct phrase for land-based flags is “half staff,” as reflected in the links in this post. Flags flown at sea would be at “half mast,” as in the mast of a ship.