I'd rebooted one of controlled server and had strange situation: /tmp becomes full of uploaded files. move_uploaded_file works as expected, PHP and Apache error logs are empty (there was some Warnings that does not relate to this problem).
I tried to found the reason, so I change upload_tmp_dir to /tmp/uploads in php.ini and restart Apache. After that "lsof /tmp" outputs strange log:
php 29007 webuser 17r REG 0,22 389161 52039971 /tmp/webuserjReqqp
php 29007 webuser 17r REG 0,22 311739 52042859 /tmp/webuser1SGrJK
httpd 1146 webuser mem REG 0,22 1169082 52053441 /tmp/uploads/phpJAiz0F
httpd 1146 webuser 15u REG 0,22 1169082 52053441 /tmp/uploads/phpJAiz0F
php 29007 webuser 17r REG 0,22 316849 52056728 /tmp/webuseriCSUB4
php 29007 webuser 17r REG 0,22 324447 52056931 /tmp/webuserJIWgw2
php 29007 webuser 17r REG 0,22 1591592 52059078 /tmp/webuserIJm88x
So PHP works with /tmp/uploads as expected, but why Apache creates files in /tmp?