…es", caused by cookielib. Also documented a workaround if absolutely necessary.
When a PreparedRequests's cookie jar is not a RequestsCookieJar instance, it will not have a "copy" method. By adding _copy_cookie_jar we can reliably copy cookie jars so that we have an actual copy instead of the same instance on different prepared requests. This also updates the RequestsCookieJar.update logic to create copies of cookies from the other jar. Closes #2527