I'm using the AutoCompleteBox with an Array datasource with about 1000 items. The minimum search limit is 3 characters.
When typing for example "JOHN" with a somewhat lower pace, the Postback fires as soon as the "H" is typed (third character, as expected).
If you continue typing the "N", another Postback fires.
However, the resulting drop down list is the result of the first query and shows items that do not match "JOHN". The results of the second Postback are discarded. The user must now add or remove characters from the search string to get the desired result.
It seems that there is a problem with this control, which causes subsequent Postbacks not to be handled correctly. It would also be nice if it would be possible to control the timing behaviour, for example to set a higher value for the time that must pass before a Postback fires.