SelectBoxEditor wit Data Source

Hi,

I’ve got a similar problem, but even more mad:
One can assign a value to the attached property of the page using the selectBoxEditor.
In my case the value is an identifier for my “project domain model”.
The plugins I wrote, which are using this value work just fine.
The first option of the selectBox is empty (“Please chose …”).
If one chose the page with the SelectBox in the tree, in about 30% - 40% of the cases the SelectBox displays the correct value. The rest ist “please chose”.
Any hints for me?

Thanks in advance
Klaus