The current workaround is to directly set the value of the underlying TextBox instead: this.RadAutoCompleteBox.ChildrenOfType<TextBox>().First().Text = "1 I";
When you start typing, the dropdown appears and then you leave the AutoCompleteBox without clicking, the cursor is not changing back to arrow. As a workaround of the issue you could manually release the mouse capture in the Populated event handler of the control as shown below: private void AutoCompleteBox_Populated(object sender, System.EventArgs e) { if (Mouse.Captured is RadAutoCompleteBox) { (sender as RadAutoCompleteBox).ReleaseMouseCapture(); } }