the last timezone (you have selected) is stored on the server in a DAV property (and after you login, the previous settings are applied). If you login as a new user (or remove the settings stored on the server) you will see the new timezone preselected.

You can also login using shift + click to the login button, and the settings stored on the server will be completely ignored.

Also don't forget that each time you change the config.js you need to execute cache_update.sh (otherwise the change will be ignored, and the previous config.js will be loaded from HTML5 cache).

JM