graphic library 4D/50GT 4D/120GTX

[Eric Hoffman]

I have written an application using the Iris fortran graphic library.
I compile it using the -lgl_s and -lfgl options of the fortran
compiler. For some strange reasons, it works fine on a 4D/50GT but
behave strangely on a 4D/120GTX (I recompiled the code on each machine):
Some of my drawings (lines, axis) keep on flashing on and off in some
erratic manner. 
Any clue of what's going on?