If you have page jumps to named positions (<a name=…), when you jump in the same page, the wordpress.com admin bar hides content (for example title or subtitle, which is at that named position). If you jump to the anchor from another page, the page contents are shifted down and text is seen.
I have made a test page to demonstrate this. If you jump to http://testipeti.wordpress.com/about/#2 you see the title “2. This is a very long page.”. But if you use the links in the page, the title goes always (at least partly) under the wordpress.com admin bar.