Vaadin application loss of CSS styling before display change

I'm developing vaadin application with a home page and a multi tab view.

On the home page there are two link buttons shown like this 'Login | Register', i.e. with some spacing and separated by a pipe character. When I click on 'Login' what happens whilst still on home page and just before the login screen is displayed is the spacing between the two links and the pipe char is lost like so 'Login|Register' and hence they appear to have lost position then the login page is displayed.

This kind behaviour is observed throughout the application and not just on the home page, i.e. the behaviour of items on screen changing position just before changing display.

My best guess why this is happening is that for some reason the CSS styling is lost a second before display change hence causing the slight position movement.

This is rather annoying as it seems the view flickers just before view change.

Any ideas why this is happening and how to stop this behaviour.