nview playing silly buggers

I had this problem last year, now its occurred again (then with a nv7600gs, now I have a nv9500) both times winXP

by turning on nview like so
nview - nview properties -> nview desktop manager -> enable (no transparency etc, I just use it to I can make a window be ‘always at front’)

one of my gl apps goes all to buggery, my apps cpu usage is the same both times (~25%). its like nview is somehow stealing some of my gpu cycles

heres the framerate for the same scene, one with nview enable + one without

any insights?
cheers zed