I categorize this as bugs caused by data inconsistency because od data duplication. That includes:

- Using asynchronous database replication and reading data from database slaves - Duplicating same data over multiple database tables (possibly for performance reasons) - Having additional system that duplicates some data. For example: in the middle of rewriting some legacy system - a process that was split into phases so functionality between new and old systems overlap for some period of time.

Based on my experience I always assume that inconsistency is unavoidable when the same information is stored in more than one place.