Indicate somehow that the for the search box to disappear you need to click the search button on the top right (When we use the filter in the calendar you can see an empty and filled icon)

It still happens on 4.1, a user see this:

To hide the search bar they need to tap on the magnifying glass.
IMHO it would be cleared if the magnifying glass had some grey background or something to indicate you need to tap there. Something like what is shown to remark you tapped there:

Take into account that on calendar there is no more empty and filled icon for the filter so maybe this is not feasible