keystone rc source file not working for API v2

I am testing RHEL7.3 based OSP 10 using packstack, the default keystone API version is v2 in answer.txt,

CONFIG_KEYSTONE_API_VERSION=v2.0

so will generate keystomerc_admin after packstack running,

unset OS_SERVICE_TOKEN
export OS_USERNAME=admin
export OS_PASSWORD=demo
export OS_AUTH_URL=http://188.28.88.11:5000/v2
export PS1='[\u@\h \W(keystone_admin)]\$ '

export OS_TENANT_NAME=admin
export OS_REGION_NAME=RegionOne

then got this error for all openstack command,

openstack --debug server list

OpenStackConfigException: Missing value auth-url required for auth plugin password
clean_up ListServer: Missing value auth-url required for auth plugin password

However when I changed keystone API to v3 in source file, openstack command working well now,

export OS_AUTH_URL=http://188.28.88.11:5000/v3
export OS_PROJECT_DOMAIN_NAME=Default
export OS_IDENTITY_API_VERSION=3

The interesting point is keystone endpoint is v2.0 but need to config as v3.0 to access it ,

openstack endpoint list |grep keystone
| 8bf9e1f995124dce906398ad68817fc5 | RegionOne | keystone | identity | True | admin | http://188.28.88.11:35357/v2.0 |
| ec89afa624e24ba7ad9404bbca3beef5 | RegionOne | keystone | identity | True | public | http://188.28.88.11:5000/v2.0 |
| f459682583c14920a20ece5fad7b86ae | RegionOne | keystone | identity | True | internal | http://188.28.88.11:5000/v2.0 |