Someone's run a switch to simple recovery and back to full since the last full/diff backup. It'll be logged in the error log.
p.s. Are you sure you want those DBs in bulk-logged recovery all the time?
http://www.sqlservercentral.com/articles/Recovery+Model/89664/
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