Particle Flow Access

Hi. Well, my problem is, I use the

$PF_Source_01.updateParticles PF_Source_01 framnumber

code to update a changed Rand Seed on the Particles Position.
That works very well. But when I integrate that same code snippet into a rollout dialog like

rollout test_rollout "Particle Randomisation"
(
button btn_randomize "Randomize"
on btn_randomize pressed do
(
$PF_Source_01.Event_01.Position_Icon_01.newRand()
$PF_Source_01.updateParticles PF_Source_01 framnumber
)
)
createDialog test_rollout widht:xxx height:xxx

it does not update the particles. where is the problem?