I’m using environments (Production, Development, etc.) for a project.

All events created on one appear on the other, except custom events.

Custom events as specified on 

https://help.amplitude.com/hc/en-us/articles/360047138392#create-a-custom-event-from-existing-events
https://help.amplitude.com/hc/en-us/articles/360041885332-Group-two-or-more-events-together-as-a-single-step-in-the-Events-module

Seem attached to just one environment, despite the underlying events existing on both. 

Is there any way to share them or promote them between envs?

Having to recreate them on each environment would make them quite difficult to use effectively.