AutocompleteBox: cursor jump to the end of text when editing

[Se7enleaves]

IsTextAutoCompletionEnabled=True
Filtermode=Contains

When the autocompletebox starts to autocomplete based on the input text, the cursor would jump to the end of the text after typing in one letter if the user move the cursor to the middle of the text and try to edit the text.

For instance,

For a input text of ‘TEXT’, the returned autocomplete is ‘TEXTAUTOCOMPLETE’.

If I want to add ‘123’ in between ‘TEXT’ and ‘AUTOCOMPLTE’ by moving the cursor to right after ‘TEXT’.
When typing in ‘123’, ‘TEXT1AUTOCOMPLETE23’ would be the result due to the jump of cursor.

The problem doesn’t occur if users select a autocomplete item from the lists then make changes to the selected result.

Could you fix the problem?