[jQuery] [autocomplete] every item shown regardless of letter typed

Hi!
I'm using Jörn Zaefferers autocomplete, and happy day, using json as
datasource is working!
Sadly, I have not reached nirvana yet....
When I press a "s" for instance, the goal is of course to only show
the items starting with "s". But no, every item is shown!
What can cause this?
Thanx!