I just checked, and you can choose to sell or store the existing module when you buy a new one for that slot. The default is to store it, which is as it should be - you don't want to accidentally sell an engineered module.i don't like the idea of buying new modules and they don't automatically sell the old one, they store them, and you then have to go into stored modules to sell them
old way was better
Pretty sure that's the same behaviour as the old version, even if the UI interface has changed.