Why doesn't PS CC save changes to a smart object?

Question

Adobe Photoshop

I edit the smart object, add a couple of layers, press Ctrl + S, and Photoshop offers to save the smart object to a separate file. And you need, as usual, in mockups - you pressed Ctrl + S and the changes were immediately saved in the main file.
I rummaged through a bunch of information, but did not understand the patterns: it saves in some files, not in others.