text appearance changes if I save as *.htm

[C.M.G.]

PowerPoint 2003
Windows xp pro sp2

When I save a .ppt file as htm, the appearance of animated text sometimes
changes: the
letters have coarse, rough edges (they sort of look like somebody had cut
them out with an acetylene torch...).

This change is unpredictable and appears to apply to the whole slide. If I
save the .ppt file a second time (again as .htm), the text on a different
slide might be changed.

Any idea why this is, and how to fix it?

Thanks,

Clem.