Yes, as I mentioned in an earlier post, I really like the help design on your web site. I researched many looks in preparing for a new stylesheet project. Ended up emulating a lot of your elements rather than reinvent the wheel.
Hope you are OK with that. Imitation is the sincerest form of flattery (definitely in my case).
Anyhow, I figured out my problem. The CSS for my original tables was using 5px padding all around. In Word output, this gets converted to table cell margins.
And that's what the PDF conversion doesn't like. Take out the original CSS padding--or the converted Word cell margins--and the problem goes away, leaving clean unbroken table lines in the PDF.