I think newer versions of browsers are more sensitive to this. I did a RoboHelp class in Detroit and one of the complaints was "missing" text, despite it being there When we looked at the source HTML, there were span tags galore with transparent applied. I think it's something RoboHelp did when they cleared formatting or something.
This would beg the question of how it managed to get into the style pod.
It's possible that you or someone had some manual formatting with the transparent stuff in there and attempt to re-apply Normal and you saw the following dialog:
Cheers... Rick