composer: get version error with HTTP_PROXY_REQUEST_FULLURI=false

When I set HTTP_PROXY_REQUEST_FULLURI to false with proxy. I get this error:

composer.phar --version
Composer version 5d360ab43b3e3bc29bbce969a2574ae1e7080fbf

composer.phar diag
Checking platform settings: OK
Checking http connectivity: OK
Checking HTTP proxy: OK
Checking HTTPS proxy support for request_fulluri: OK
Checking composer.json: OK
Checking composer version: OK

composer.phar update -o
Loading composer repositories with package information
Updating dependencies (including require-dev)
The "http://packagist.org/p/kriswallsmith/assetic$e3d5f0722930c4c2f6bd90a5e13c1a50644071a02d02efc41eec3374bb29bc5e.json" file could not be downloaded (HTTP/1.1 400 Invalid header received from client)
http://packagist.org could not be fully loaded, package information was loaded from the local cache and may be out of date
Generating autoload files

when I remove HTTP_PROXY_REQUEST_FULLURI, I can not install/update https vendor, and I get this error:

composer.phar diag
Checking platform settings: OK
Checking http connectivity: OK
Checking HTTP proxy: OK
Checking HTTPS proxy support for request_fulluri: FAIL
It seems there is a problem with your proxy server, try setting the "HTTP_PROXY_REQUEST_FULLURI" environment variable to "false"
Checking composer.json: OK
Checking composer version: OK

seems HTTP_PROXY_REQUEST_FULLURI only use for download vendor, not use for get version information from packagist.org site.