See, that's the kind of mean spirited reading of texts I hate so much. They were made aware of the issue, they looked at the code and (they claim) that it doesn

See, that's the kind of mean spirited reading of texts I hate so much. They were made aware of the issue, they looked at the code and (they claim) that it doesn't behave as designed because of a bug. This is them saying "We didn't design the cache to never be purged, that's a bug." Whether you believe that or not is your own problem but that's the whole story, writing "a bug we uncovered" is entirely appropriate in that context.