Like I said, 20 innings. It's like when Phil Gosselin had a 1.000 OPS for four weeks. Or Harper having a .486 OPS in his last 21 games.
You have to take the longer view, and the longer view says Gosselin is still a AAAA player, Harper is still an all-star, and Hembree is a competent if not above average major league reliever going through a bad patch. On a team that forces relievers into situations where they can't succeed, as well as a season that make fans overreact because it's September 20 instead of May 20.
If it was May 20 he'd either come around or actually would get cut. But it's still not an easy call. If we'd kept every reliever we had on last year's team from August 1 we might actually have a better bullpen now, but nobody wanted that either.