When I test my games some data is saved as names, highscore etc. After the export the game with Node Webkit and make a release, data from testing is there. I can make a cleanup manually, sure, but, I think the data must clean from local storage before export the game automatically, 'cause probably this data keep in another projects because it is the same nwjs window preview and export, I think.
Steps to Reproduce Bug
LocalStorage generated on preview mode persist after export
LocalStorage empty after export
Operating System and Service Pack
Windows 10 Home
Construct 2 Version ID
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It might just be your own browser doing that. do you have a buddy computer to test the theory out try to get him to play test the game to see if it saved on his?
I think NW.js uses the project name as the storage key. I've made it different in preview mode for the next build which should fix this.