The border attributes (and some others) are right now rendered as HTML attributes rather than CSS code - this makes it hard to override them by Stylesheets. E.g. the default value for the border attribute is "1", so if not explicitly specified otherwise, it will turn out as <img border="1" ...> in the page, which causes nasty red boxes around. Would be nice if that could be changed to <img style="border: 1px; ...> instead.
This is affecting Trac 0.10 *and* 0.11 versions.
Funny: On the 0.11 installation we tapped into that, it seems that only Screenshots affected when no align was explicitly defined...