How to persist the original user input after populating the Dijit ComboBox

I have a Dijit ComboBox which is dynamically populated once a user enters a search term. When the user hits enter, the search term is sent to an external web service, a JSON list is returned and stored in an ItemFileWriteStore which is then used as the "store" to populate the ComboBox.

This all works fine except for an extra requirement. I'd like the original user search term to appear in the input of the ComboBox. This is in case the user realized they entered the wrong search term and are then able to modify it without needing to type out the whole text again.

I am doing:

dijit.byId('searchTerm').set('displayedValue', userInput );

But I see that the displayed value is only displayed for a split second before going blank again. Can someone tell me what I am doing wrong or even if my requirement is even possible?