It's a theory.
It's not a bug.
Because... one possibility - it's not the same item. I wouldn't be able to tell.
Another possibility is - something I wouldn't know for sure but can test. The deterioration would still be a subjective view (due to lack of personally keeping track and not a single success yet).
Both possibilities based on theories which are based on observations of other stats. The point of which, if one stat changes, other stats possibly change too.
