As a singer this infuriates me. Hey, by the recessional I'm tired, I don't always feel like singing it. The least these people can do is stick around till it's done. If I'm not mistaken, the Missa, Ita Est doesn't come until after the hymn. Or maybe it's before, at any rate, it's direspectful. At the liberal parish I started at, there was a lot of this. At the Anglican Use parish I'm at now, nobody budges.
Our Lady of Walsingham?