Sneaky rollback in SQL Server 2008 R2 Is it possible for an entire set of committed transactions to be rolled back in SQL Server 2008 R2 without any notification or logging anywhere?

We had a set of data apparently get rolled back this weekend on an HA cluster SQL Server 2008 R2 environment. Data existed and now it doesn't. Nothing in the SQL Server error logs, nothing in the cluster logs. SQL Server agent job that originally loaded the data ran successfully (including progress emails sent from the processes themselves).

The only thing that wasn't rolled back was the bulk inserted data. The database is set to full recovery, so bulk inserted data SHOULD have been rolled back as well, correct?  

Sorry for the lack of details but I am THOROUGHLY stumped. Can't even think where else to LOOK.
As Remus succinctly puts it, there is no secret feature to rollback a transaction without logging. It is also not possible to rollback a committed transaction.

Your code is broken, not SQL Server.

From the scant details the only scenario I can envisage is the now missing data having been inserted as one long running distributed transaction, someone sighting the data via an uncommitted read and the transaction subsequently being rolled back.

Most likely is an error in the logic or analysis of the failure. Human error and cover-up perhaps even more so.