Has the DB just been switched from full or bulk-logged recovery? If so, run a checkpoint, sys.databases is not updated immediately, hence you can get 'log backup' occurring for a very short period after the DB has been switched to simple recovery model.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability