Much ado about nothing. If you have to set environment, do it at the beginning of a program, before threading. When you execute an application, pass a new environment, without setting it. There's really no need to set environment from threads.

The only use case where this bug happens seems to be threaded programs that load libraries after threading has initialized, and want to configure those libraries with environment variables, that the user/parent program hasn't specified, rather than calling their APIs with specific arguments. If a library provides no way to set some option other than environment variables, their API is simply incomplete and needs fixing. An incomplete library is not a good enough reason to amend the C standard.