It's been a historical fact that when Google Sites gets some updates or upgrades, it starts acting a little funny. That's why I'm here to give you a bug report and note some changes occurring.
Before today, you could add "spacers" into the horizontal navigation bar by Adding a URL, Hitting Space Bar for the Title, and putting a URL in the Web Address Field. No link would be visible or Link Title, but it would add some space between two normal links.
Now, if your Link Title has just spaces, it will display the Link URL you put in. Therefore, you can't reasonably space out your links with this method anymore.
So far it is not retro-active, affecting your existing spacers.