Thanks for writing.
According to our tests our ExpanderControl integrates with DataBoundListBox very well. We have tested different scenarios with thousands of items in the data source applied to the listbox and haven't been able to reproduce any undesired behavior.
We are willing to take a look at your code so is it possible for you to prepare a sample project that demonstrates your scenario and send it to us for further investigation?
You will have to open a new support ticket in order to be able to attach your project.
Thanks for your time.
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