Incorrect Target Loudness With Match Loudness?

[KenTheriot]

I have a spoken-word vocal file that I want to set to a loudness of -16 LUFS. In the past, I've simply run Match Loudness, chosen ITU-R BS.1770-3 Loudness, and selected "-16 LUFS" for my Target Loudness. And then I run Amplitude Statistics on the result to verify it is, in fact, now -16 LUFS. 

But I just did that today and even though I set the target Loudness to -16 LUFS, the resulting file is only -17 LUFS. Why is that happening? Why isn't it -16 LUFS? This is very strange.

[KenTheriot]

Just as an experiment, I converted the original mono voice file to a stereo file and tried Match Loudness again. And Bingo! This time it DID result in a -16 LUFS file.

So why did that work? Not understanding something here.