Problem with Jquery UI Autocomplete, using the Delete-Key

Problem with Jquery UI Autocomplete, using the Delete-Key

Hi folks,
 
i just implemented the Jquery-ui Autocomplete with the parameter "minLength: 2". But I ran into trouble whenever I use the "Delete"-Key:
 
- I type two letters into the autocomplete field (for example "as") -> The autocomplete-list opens
- Then I delete the "s" and type it again -> The autocomplete list doesnt open
 
I found this problem in the official demos, too: ( http://jqueryui.com/demos/autocomplete/)
 
Any Ideas how to solve this problem?