OK, how about we have a look at what is really going on with the files in both places. Run these, and post the results:

restore filelistonly from disk ='C:\MSSQL\Backup\DEV-database'+ (select CONVERT(VARCHAR(8), getdate(), 112))+'.bak'

select name, physical_name

from Dev_Database_Test.sys.database_files

You may want to run the second query on the source database, as well, just to see if someone added a fourth file on you.