Synchronize module ignores ansible_user parameter

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I got same problem (https://github.com/ansible/ansible/issues/29483) for Ansible 2.7.5 and 2.5.1.

Only difference is that password prompt is hidden and thus, the task hangs continuously.

that is, when sending a file from remote server A to remote server B,

the synchronize module's trying to connect to B with same username used when connecting to A.

Does anyone know how I can use different username when connecting to B.

used ansible versions are as follow, 

ansible 2.7.5

  config file = /etc/ansible/ansible.cfg

  configured module search path = [u'/home/test/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']

  ansible python module location = /usr/lib/python2.7/dist-packages/ansible

  executable location = /usr/bin/ansible

  python version = 2.7.12 (default, Nov 12 2018, 14:36:49) [GCC 5.4.0 20160609]

ansible 2.5.1

  config file = /etc/ansible/ansible.cfg

  configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']

  ansible python module location = /usr/lib/python2.7/dist-packages/ansible

  executable location = /usr/bin/ansible

  python version = 2.7.15rc1 (default, Nov 12 2018, 14:31:15) [GCC 7.3.0]