slow framerate on second monitor

hello all,

i have found a strage behaviour concerning the jit.window.
if i send it a rect message to move it to my second monitor,
the framerate slows down from 60 to 30. the window has the same
dimension on the main monitor and second monitor.

the hardware is a macpro with 2 identical graficcards.

the only way to get the frqamerate of 60 is sending a border 0
and one second later a border 1 message.

the message window is reporting:
building GL on window "myOutput"

hardware: macpro4,1
software: mac osx 10.6.4, max 5.1.4

perhaps someone can tell me, what i am doing wrong ....
or point me to the right way to move a window from one
GPU to another.

thanks in advance,
gisela