SQL Server version 11.0.3128. I have an automated process (job, stored procedure) that inserts DMV data into database tables every half hour. It has run without incident for well over a month. On Nov. 14, the 19:20 run failed with 46 instances of "Violation of primary key constraint ... cannot insert duplicate key ..." into one of the tables. The key of the table is an identity, type integer, start 1 increment 1, values attempted for insert 317211 - 317256. The 19:50 run ran fine.
Looking at the table I can see rows with the identity column, values 317211 - 317256, timestamped at 18:50. Looks like the error message is valid, the identity key values attempted for insert were already used.
There is a daily job running at 19:00 that takes 5 or 6 minutes, it runs dbcc checkdb, reorgs all indexes, and updates all statistics, for many databases.
Did I happen across a rarely-occuring bug?