Go to the corresponding data feed. Check the result is okay. Press the save button.
MashApp reacts like before.
Hint: If you use MashApp -> edit FeedEditor, this does not help, because there is no save button.
what did you mean by "use MashApp -> edit FeedEditor"? Did you mean switching into the data feed editor directly while assigning data?
In this case you will be asked to save the feed after hitting the Back to Composer button.
I mean this page. If you do no "relevant" changes in the data feed editor ( example :moving the elementare not recognized as a change) and you press "back to Composer" , you are not asked to save the changes, because no "relevant" changes happened.