I have encountered this bug in IDL. you can use this code: window,1 x=findgen(100) y=findgen(50) y=[y,reverse(y)] plot,x,y,yr=[0,100],/ys window,2 plot,x,y,yr=[0,150],/ys ;here you change the yrange wset,1 ; here you call back window1, but NOT its yrange !! oplot,x,y,color=100 If you look at the result the oplot is not the same, because it remembers the yr of window 2 and not wset,1.  Problem encountered on a linux machine (Ubuntu 9.04 - the Jaunty Jackalope) Beware when you plot several variables and you need to use wset!!