(2.0) Tooltip flashes black before displaying

hi,
i have a multi-line tooltip, about 10 lines long.
when it is displayed, it gives off an ugly black flash on the screen
before rendering correctly. it is very noticeable. what can i do to
lose the flicker?

i've tried it with the IsBalloon property on and off and the behaviour
is the same. It is also unaffected by any combination of UseAnimation
and UseFading.

thanks
tim