I guess I found a bug:
In Ajax Search Pro -> Layout options -> Results layout:
I deactivated “show author in results?” -> no Author shown everything is fine
I deactivated additional “show date in results?” -> Author and Date is again showing.
And since that Author and Date is shown all the time, I can’t deactivate it anymore…
New information:
If I deactivate author and date, and duplicate that search instance it work for the new instance.
So in the new search instance author and date is hidden, but you have to set design in theme chooser again.