嵌套ListBox与DataTemplates的边距差异

I have a problem with my ListBox. I have written several DataTemplates which I use in a ListBox. Each one of these contains a grid and may contain a nested ListBox depending on the item. My problem is: The height of these nested ListBoxes seem to be different to the root ListBox's height. Additionally it seems, that there is sometimes one pixel margin to the element above.I have a problem with my ListBox. I have writte