I recently encountered some very strange behavior when using Amarok 1.4.10. I had just made a copy of two new albums I had purchased, trying out a new (to me) codec. I was using Vorbis, in an Ogg container. The standard file extension for these types of files is .ogg or .oga which stands for Ogg Audio. The default in the "Juicer" program I was using was to store the files as .oga. After I was finished ripping the disks to my music collection, I told Amarok to update my collection with the new files.
I was unhappy to find out that even after completing the update, my new files hadn't been added to my collection. I thought it had something to do with the fact that these were Ogg Vorbis files, so I attempted to manually ad them to a playlist. This worked fine, but when I attempted to edit the title information (the artist was missing), Amarok told me it couldn't edit the file. I was a little frustrated so I gave myself some time to think over the problem.
As I continued listening to my music collection, I noticed that I had other .ogg files that played fine. On a whim, I tried renaming some of the files I had copied from .oga to .ogg and re-adding them to my playlist. Suddenly the metadata was correct and I was again able to update the track information. I also updated my collection again and the files were found.
In the end, even though I didn't touch the files I was using, Amarok was unable to read them when ending with a .oga extension, but worked with them just fine as .ogg files. I hope this saves someone else a few minutes of frustration.