automatic rollback?

After using PostgreSQL 8.1 and earlier versions for years, I'm suddenly
encountering a vexing problem. A certain kind of update and insert is
frequently reverting to its original condition after a day or two -- the
inserted record is gone and the updated one is back the way it was.
There seems to be no code in the application that could be doing this.

I know this is a long shot but is there any way the changes could be
getting rolled back automatically? I'm not using any explicit COMMIT,
ROLLBACK, or SAVEPOINT statements.

John Gunther