array_diff_assoc converts values to strings. Perhaps we need to use array_udiff_assoc that also diffs the values.

What we want is to get list of message groups with key additions / deletions to purge the completion statistics (as last resort, ideally all the operations that handle these changes would clear the stats themselves - this also misses content changes, but those usually cause page changes which should clear stats for affected groups).

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Severity: normal