ftp.yz.yamagata-u.ac.jp mirror unreliable

The following link is returning 404 Not Found most of the time:
http://ftp.yz.yamagata-u.ac.jp/pub/qtproject/official_releases/qt/5.2/5.2.1/submodules/qtbase-opensource-src-5.2.1.tar.xz

However if you keep trying, the download will actually start working.