... . For your own safety, if you can actually identify the point where the bug happens, make a save before it happens. Do not save over old saves after the point where the bug occurs. In practical terms, make sure that after an update your first save is a new one, and don't overwrite old saves.
Your advice is correct. As a programmer myself, i can agree to the most you said in general, even i don't see "coding errors" as "bugs" - but let's not keep going off-topic on this minor issue...
Regerding the saves, i always do a new savegame once i reached into the new content and never overwrite the old saves. And i save frequently though.
My words, which i always tell my programmer students: "No backup? -> no mercy!" XD
Thus said, i can tell that from all my old saves, this issue occurs to me, whilst a new game worked absolutely fine.
I don't know why, but somehow all of my old savegames are corrupt, but as it took less than a minute to fast-skip through the game, it's not worth to unpack the archives to have a look into the isue any further.