Grammar question

[Cloud]

Heya, I'd like your opinion on this:

I'm reviewing a brief right now, and there are several sentences with this construction:

"The only evidence were the affidavits."

Now, to me, that's incorrect agreement between the subject and verb. If "evidence" is the subject, then it should read, "The only evidence was the affidavits."

But that sounds wrong. Maybe "evidence" is a collective noun? Maybe the verb "to be" is reflexive and is messing me up.

If you reverse it, to say "The affidavits were the only evidence" that sounds better, and I could reword it. But I was always taught that the sentence construction should be the same either way (subject first, or object first, you still have to have agreement.)