Cell borders overlap text in merged cells

I created a Numbers spreadsheet with some text in some merged cells.

When I saved a PDF, there are white lines through the text where the original cell borders were. Here's what it looks like:

If you look at the word "The," you can easily see white lines running through the letters. One the letter 'e' you can see both horizontal and vertical lines.

How can I fix this? If it's a bug, is there a workaround?

You can view the original document, and even download it at this linked page.