Synchronize module ignores ansible_user parameter

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]