Input_AutoComplete_GetIdentifier retaining identifier

I am using Autocomplete widget and I have an issue with the validation for invalid input.

1. If I type invalid value initially Input_Autocomplete_GetIdentifier retunr empty string (I expect -1 ???)
2.If valid entry is selected and then new invlaid value is typed in identifier will return last valid selected identifier (retaining old valid id) instead -1.

PreviousIdentifier property is set. This is V. 9.0.1

Any hint or advice how to do this properly?

What about using the Select2 widget from silk UI? Did you tried it already?