Auto-sync with timecode only works in 24p

I have a GH5 and Mixpre-3 connected by HDMI. When I record and bring in the clips, I find that the auto-sync with timecode only works when my clips are recorded in 24p. I have tried this with the camera set to 4K as well as 1080. The Mixpre-3 is recording at 48K/24-bit. When I use 30p video, the audio track seems to be sync'd 6 frames ahead of the video. This is true in both Resolve 14 and 15b1 and 15b2.

If there was a Groucho Marx emoticon, I'd say "So stop recording in 30p."