We're preparing to move to Confluence 5.1.3, and in our test installation, one of our pages does something very strange -- when you go from the editor, either saving or cancelling, the page displays briefly, then immediately redirects to a garbage address "data:text/html,<p></p>". That looks like there might be an extra quote mark somewhere when the HTML is rendered.
I've tracked this down to an HTML macro that has some fairly complex HTML in it, but does not have an extra quote or other errors. This does not happen in version 4.0.4, our previous version.
Note that this DOES NOT happen when simply going to view the page, but only when you edit the page and either cancel and save.