SDK AE arbitrary params data flow

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