Help! Weird Melodyne behaviour

I've used Melodyne a million times for vocal pitch correction. It's awesome. However, today it is doing something really odd and I can't work out why.
 
When I highlight my vocal clip and turn it into a Melodyne clip it massively reduces the volume of the clip. I'd say it's taking a good 12dB off the clip. I now have a quiet weedy waveform when I had a nice healthy one before. Any ideas why this might be happening?