[Bug] Winui's Combobox changing size when popup open

Combobox layouts look fine in their default view:

When clicked the anchor moves and breaks the layout:

This is especially noticeable if the combobox is wider:

It's almos as if the underlying element changes its width when clicked.
The same does not occur in the Windows settings, so is it a framework bug that we can't do anything about?

Windows settings:

Any ideas @ChenYiLins @Jay-o-Way? Should we even bother looking into this?

Start by reproducing the issue with the WinUI ComboBox examples shown in the report, comparing the closed and open states and the wider layouts. Investigate whether the anchor or underlying element changes size when the popup opens; done means the layout remains stable like the Windows Settings comparison.

Written by the indexing model from the issue text.