popup won't stay if PopupMode="MouseOver" and StaysOpen="True"

this simple markup illustrate the issue
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A
B

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as soon i leave the trigger button the popup hide so i cannot select an option from the listbox .

and here a gif showing how it looks :

Reproduce the issue using the provided PopupBox XAML with PopupMode="MouseOver" and StaysOpen="True". Start by tracing the PopupBox mouse-over and popup-closing behavior; done means the popup remains visible when the pointer leaves the trigger so a ListBox option can be selected.

Written by the indexing model from the issue text.