blinking clists/ctrees

[Markus Lausser <sgop users sourceforge net>]

HEllo.

In my application there is a notebook. It has got serveral pages with clists
and ctrees.
Now i added a new page with some drawingareas in it. Every second i draw
something into the areas no matter whether this notebook page is visible.

SInce i added the new page all my clists and ctrees in the other notebook
pages began to blink every second (i suppose it is a new expose event ). 
Why does this appear? and how do i avoid this?
Should i only draw into a drawingarea if it is visible?