customBodyRender firing twice

Is there a reason why customBodyRender gets called twice? I noticed it on my current project, but then reproduced it on a sample project that I found.

I forked from someone elses code and added a console.log, you'll notice it is being called twice.
https://codesandbox.io/s/p5m1m1kwwq

The first time it appears that updateValue is undefined, and the next time it has a value. My use case is probably different than most, as I am updating state depending on the row (infinite scrolling).