KiCad does not modify your own libraries, unless you tell it to (Such as migrating libraries).
Do you know how Schematic Editor / File / Schematic Setup / General Field Name Templates? Anything you add there “appears” to be fields added to all symbols, but they do not really exist unless you fill in the value of the fields.
There may be things in those field name templates if you get a project from an external source.
Thanks paulvdh - when KiCad offers, I do tell it to migrate my libraries. I assumed that this is required for compatibility reasons? Maybe that is where these fields are being added but I have not done the migrate libraries thing in a long time so I don’t think that’s it.
Have you tried opening these symbols/footprints from the library (not from your schematic/layout) into the Symbol/Footprint editor to see if they have actually been modified ? or are you just going by what you see in the Schematic/Layout editors ?