Breaking down features doesn't help if two features are simply incompatible with each other. I experienced this once, when feature A that was about 3 years old

Breaking down features doesn't help if two features are simply incompatible with each other. I experienced this once, when feature A that was about 3 years old prevented feature B that was a out 1 year old from functioning correctly. The error lead to accumulation of garbage in a DB and was spotted when said DB ran out of disk space. It was incredible difficult to convey the message to management that the bug was at a meta level because both features worked as specified. They really struggled with the concept. It simply didn't fit their view on reality that features aren't completely independent.