Operators like \sin, \log, ... should be separated from their argument by a
space. TeX does this automatically, but texvc puts no space there in HTML mode:
<math>\sin x</math> is rendered as <span class="texhtml">sin<i>x</i></span>,
which looks wrong. It is impossible to work around this problem by inserting an
explicit space, because <math>\sin\,x</math> forces PNG.