SQL 2008 Change recovery model resetting from Simple to Full

I found a job running at 3am every night with the following:
enter code hereALTER DATABASE GBC_Reporting_3
SET RECOVERY SIMPLE;
GO
-- Shrink the truncated log file to 1 MB.
DBCC SHRINKFILE ('GBC_Reporting_3_log', 1);
DBCC SHRINKFILE ('GBC_Reporting_3_log' , 0, TRUNCATEONLY)
DBCC SHRINKFILE ('GBC_Reporting_3_2', 1);
DBCC SHRINKFILE ('GBC_Reporting_3_2' , 0, TRUNCATEONLY)
GO

We had to add the following to fix the problem.
-- Reset the database recovery model.
ALTER DATABASE GBC_Reporting_3
SET RECOVERY FULL;
GO

Under the simple recovery model differential backups can only have a single base. You can have multi-based differential backups (see Working with Multibase Differential Backups for some details) using the full recovery model.