Combobox AutoComplete Limit SearchFunc

[Codely2018]

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

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Windows version

No response

Additional context

No response