Ravines are only half generated if intersected by rivers

What I expected to happen was...:
...a normal ravine, with the water from the river flowing inside.

What actually happened was...:
...the ravine did not generate properly inside the river biome, and appeared filled/cut. No other terrain generation bugs were noted in the area.

Steps to Reproduce:
1. Generate a default world with the seed "7937886795779872661"
2. Walk/fly/teleport to x=267 z=-15.
3. Look down, you should find the river as shown in the screenshot.