I don't see this problem, at for example:
Are they by any chance using MSIE as a browser? If so read about the peek-a-boo bug (sigh)
(e.g. http://www.positioniseverything.net/explorer/peekaboo.html) although it usually appears in a slightly different way. (See also http://bugs.webwork.rochester.edu/show_bug.cgi?id=769 ).
Possible Fixes: 1. use a different browser 2. Use jsMath mode instead of images mode.
We have tried various ways to work around the MSIE problem, but haven't
found one that is will work all the time without causing other side
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