SDK AE arbitrary params

Hi,
I have an arbitrary parameter where the user can draw two polygonal curves.
So far it works a little. But I have trouble to get the arbH data correctly.

It is created - ok. I get in in ClickEvent, the user clicks, a new point is addet (background: 1)
Parameter is PF_CHECKIN_PARAM.
But then its disposed and copied again.

ArbitraryCopyFunc SRC background: 0 foreground: 0 - OK, empty polygons

ArbitraryCopyFunc DST after background: 0 foreground: 0 - OK
LoadArbData background: 0 foreground: 0 - OK
SaveArbData background: 1 foreground: 0 <-- here the point was set
DisposeArbData background: 1 foreground: 0 <- it was saved, dispose get the changed one, but why dispose?
ArbitraryCopyFunc SRC background: 0 foreground: 0 <-- but the next copy came and get the default one

And there are a lot of ArbitraryCopy events! Is this normal or a symptom of the problem.

There is no error or exception.

I need some explanations.
If you need more Info I can give them. I am using smart render approache if that does matter.

Thank you
Thomas