Please invaldiate/delete the full cache for the rendered math-tags.
After Bug 8 was fixed (go live on 9. April 2010 on the cluster) the old images are all still shown. When have a skin/user style with a non-white backgound, then it looks bad, when one math-tag has a transparent background and the other a white, because the first is rendered after the 9. April 2010.
See also bug 16719.
Thanks.
Version: unspecified
Severity: normal