ReLive recording always 10-20 FPS below set framerate. What's going on?

If I set my ReLive to 60 FPS, it will be recording at 42-50 FPS, not 60.
If I set my ReLive to 30 FPS, it will be recording at around 21-23 FPS, not 30.

 

It has nothing to do with bitrate, as I've changed bitrate all over the slider in an attempt to fix it, but it seems to have no effect on the FPS it records at.

 

I've noticed this since I've updated to the 17.X.X branch of drivers. Should I roll back to 16.X.X.?

 

My GPU is R9 270X and my CPU is FX-6300. I manage to record 60 FPS 720p AND 1080p just fine with Dxtory.