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Item Template with Combo box Causes Virtualization Rendering Issue in Dropdown

On initial load, when virtualization is enabled and a  item template is used (increasing the default item height), items in the ComboBox popup appear shifted up and not fully visible. Scrolling down and then back up corrects the issue, as the transform values are recalculated.

This behavior is due to the virtualization logic not accounting for the actual height of the templated items. Internally, it calculates the transform offset assuming a fixed item height. When the height changes due to item templates, the top value and rendering position do not align correctly.


Replication Procedure:
  1. Run the sample 
  2. Open the popup ( see the first item ) 
  3. Scroll down and scroll up ( see the issue items are shifted up ) 
Expected Output:
All items should render in the correct position initially, respecting the increased height defined by the template.

Current Output:
Items are shifted up on first render, leading to partially hidden or invisible rows until the list is scrolled and re-rendered.