When I clicked, "Download as PDF", the resulting PDF did not include tables. I tested [[List of Presidents of the United States]], [[v:Effective defense]], and [[v:Winning the War on Terror]].
When I tried the German language [[:de:Liste der Präsidenten der Vereinigten Staaten]], the corresponding "Als PDF herunterladen" allowed users to select "one column with tables and infoboxes" and "two columns without tables and infoboxes".
The tables also failed to appear when I clicked "Make a book" from either the English or German Wikipedia article on "List of Presidents of the United States".
A SIMPLE FIX: It looks like this problem could be easily fixed for all languages by making one column the default when creating PDF or a book and only allowing the two-column version by request -- and displaying more prominently the two-column warning "Without tables and Infobox".
I'm guessing your book creation feature would be used more if this were fixed.