Opus 5 / Fable - instead of implementing things one-by-one in a branch - decided to branch off and do everything from the starting point - meaning that they re-did work over and over, in different ways, and that almost nothing could merge back at the end.

Looking through the logs, it kept saying, "Wait I'm confused. I already did this." But I guess it decided, oh well, I'll just do it again instead of take a second to figure out what I'm doing...