from reading the email thread it appears this is the main issue: zeromq is looser about what ends up in master. They view master as sort of a global staging a

from reading the email thread it appears this is the main issue: zeromq is looser about what ends up in master. They view master as sort of a global staging area, and what ends up in release branches is viewed as stable/vetted code. As a result, master can be quite unstable. The people that forked wanted a more stable master, with lots of code reviews before patches end up in master.