You have got some old build, there might be some issues with that.
You can download WFA 2.0 release build(11275) from Now site and try this out.
I have tried the following scenarios and didn't find any issues,
1) changing the password for admin user, then login with admin user and login with some other user
2) changing the password for some other user, then login with that user and login with admin user
Please let us know if you still hit this issue with release build also..!