Oracle Managed Files (OMF) have many advantages, but the fact that such files could coexist in the same database with manually added (and named) ones, could sometimes lead to confusion. Situation is made worse by the fact, that there is no straightforward way (at least of which I'm aware of...or rather was - please check the comment of Mikhail Velikikh) to say if the file is Oracle managed or not. Oracle documentation seems to confirm this:
The views expressed in this blog are those of the authors and cannot be regarded as representing CERN’s official position.
CERN update, Quantum Diaries, Careers at CERN
Christian Antognini, Karl Arao, Martin Bach, Mark Bobak, Wolfgang Breitling, Doug Burns, Kevin Closson, Cloudera blog, Wim Coekaerts, Bertrand Drouvot, Enkitec blog, Pete Finnigan, Richard Foote, Randolf Geist, Marco Gralike, Brendan Gregg, Kyle Hailey, Tim Hall, Uwe Hesse, Frits Hoogland, Hortonworks blog, Integrity Oracle Security, Tom Kyte, Adam Leventhal, Jonathan Lewis, Cary Millsap, James Morle, Karen Morton, Arup Nanda, Mogens Nørgaard, Oracle The Data Warehouse insider, Oracle Enterprise Manager, Oracle Linux blog, Oracle Multitenant, Oracle Optimizer blog, Oracle R technologies, Oracle Upgrade blog, Oracle Virtualization blog, Kerry Osborne, Tanel Poder, Planet PostgreSQL, Kellyn Pot'Vin, Pythian blog, Greg Rahn, Mark Rittman, Riyaj Shamsudeen, Chen Shapira, Carlos Sierra, Szymon Skorupinski