I must confess, I've never quite understood why Keynes bringing Prices and Production into his reply to Hayek was a dirty tactic. Atypical, sure. But what is wrong with it exactly? I have no idea.
Hayek said he wasn't quite sure what to make of certain parts of the Treatise on Money. Keynes pointed out he couldn't make heads or tails of the Treatise because Hayek was making assumptions about the interest rate specifically in his review that he had used in Prices in Production. Keynes detailed what he thought was wrong with these assumptions (and what was different from his own assumptions), which of course was tantamount to describing what he thought was wrong with Prices and Production. He could have danced around the issue, but that was the clearest way of differentiating how Hayek was trying to read the Treatise from how Keynes was trying to write the Treatise.
So someone tell me - what's wrong with that? Clearly the editors didn't see a problem with it. And this wasn't published in Keynes's journal, after all - it was published in an LSE journal.