Combobox AutoComplete Limit SearchFunc

Describe the bug

I settted Combobox's AutoComplete true and IsEditable true, when I input a latter in the textbox, it auto setted the value matched first letters in the
Combobox's ItemSource even though the Combobox's ItemSource has many items matched the textbox's value。I thought mybe I can use the SearchFunc to solve this problem. But I found that when the textbox's matching first letters,It triggered autoComplete effect. Either it trriger the SearchFunc. Why I can not set the AutoComplete false but can use the SearchFunc ? I can't understand.

Steps to reproduce the bug

1.Set the Combobox's AutoComplete false, IsEditable true
2.Set SearchFunc =(param, p2) => {
var source = param.Cast<KeyValuePair<string, string>>();
return source.Where(k => k.Key.Contains(p2.ToString())).Select(k => k.Key).ToList();
};
3.Input some letters in Combobox's textbox, it can't trigger the SearchFunc

Expected behavior

when setting the Combobox's AutoComplete false, IsEditable true, if I set SearchFunc , It can trigger SearchFunc binding function.

Screenshots

NuGet package version

None

IDE

No response

Framework type

No response

Windows version

No response

Additional context

No response

Start by locating the WPF ComboBox implementation and the code paths for AutoComplete, IsEditable, and SearchFunc. Reproduce the listed settings with an ItemSource and typing input, then verify whether SearchFunc runs when AutoComplete is false; done means the expected callback behavior is demonstrated and covered against regression.