I am finding that music in hold is a bit hit and miss. Sometimes it will work and play as expected but quite a lot it doesn't. This applies to transfer, hold, queue and first person in the conference. Do I need to do anything or is it a known bug?
This issue could affect new uploads starting Sep 10, 2013, that had a wrong file extension (not mp3 or wav), and a bad format. These files were not shown in the list but the hidden files could produce silence on hold.
We have now corrected this and show all music uploads. Thanks for your report!