There are situations that arise when copy editing (and writing, editing, etc.) in which no matter what decision you make there will be someone there to challenge it.
John McIntyre, on his blog You Don't Say: Language and Usage, talks about the conundrum of choosing to use "data is" or "data are."
I know that there are people on both sides of the fence who will argue till they are blue in the face that their side is right, so I will not get into the middle of this debate.
Singular or plural can be complicated. Is one in five people really talking about one person, or is it talking about many people?
It's one of those things that just needs to be consistent in a publication. No matter which side you choose you will have your critics.