Flashing with default - how does the IDE get the .bin file and how is it delivered - could it have been cached? ...was I too quick

I have read somewhere, that when a program is saved on Espruino and we flash a new version it will maybe not work, because there are many changes in the new version. Then reset(), save() and then flash.
By the way, I had the the unreleased on my Espruino, but nothing saved, so I could do the flash with no trouble.