I recently moved my Temp database files onto a separate drive (I had two data files and one log file).
However, after restarting the server, my second data file disappeared both from the file list on the gui and from sp_helpfile. I've managed to reproduce this behaviour several times: I add a new data file, see it appear both in the gui and sp_helpfile, and disappear after rebooting the server.
dbcc checkdb against the database and it returns no errors. There's no information either in the SQL logs or the windows application event log.
After doing a little more research, I ran the following query:
select d.name, m.* from sys.master_files m inner join sys.databases d on (m.database_id = d.database_id) where d.name like 'tempdb' order by 1, 2
It shows four different secondary data files, none of which appear in sp_helpfile. If I try to use any of those names SQL server doesn't allow me to. None of these files physically exist on the disk. My server is SQL 2012 Standard.