screen font problem with 1.3.1. on RedHat 8.0

[John Ringland]

I'm a new LyX user, and have installed 1.3.1 on RedHat 8.0.

Some math symbols, such as a big sigma (sum) are not displayed.
Here is a screenshot: 
http://orange.math.buffalo.edu/temp/lyx_font_problem.gif ,
showing the display with the missing symbol, along with the output 
(which is ok).

Any help greatly appreciated.

JR