Test case:
http://hsivonen.iki.fi/test/css-latex/latex.html

This case may be underspecified in CSS, but Gecko, WebKit, Presto, Tasman and, I believe, Trident all render the test case interoperably with a normal space between the words "The" and "LaTeX". It seems that the browsers agree that letter-spacing for a given letter affects the space between it and the next letter.

With Prince 6.0 (alpha 2007-01-16) the space between the words disappears:
http://hsivonen.iki.fi/test/css-latex/latex.pdf

Workaround: wrapping the preceding space in a span that has letter-spacing: 0.