this happens in small forms with IE and using the submit button as the trigger in data assist search. The issue is that IE does not pass the submit button when a small form is submitted.
the fix is to use a different trigger. if there is only one text box in the form, use the text box as the trigger. If there are more than one, create a hidden form element in the search form, and use the hidden form element as the trigger.
If the search form is on a separate page from the results, go to the bindings panel and click the plus button, select Form Data.
in the form data dialog box, click the folder icon and select the search page.
On the Server Behaviors panel, double click the DataAssist Search server behavior. click the lightning bolt next to trigger and select the text box from the search form.