I am using #combo_filter on Header. When I select a choice, it filters correctly. But I can’t clear out the ‘choice’ and reselect.
Which version of dhtmlxgrid you are using?
When combo used in header, it initialized in filtering mode ( which means only text related to typed mask shown ) , so you need to delete entered text to see all options.
Starting from dhtmlxgrid 2.1 it was a bit improved to have clearly visible empty option in any case.