I think this may be related to the issue that people were having with the new ripping workflow.
basically what has been happening is that I will rip a bunch of cds and I know they all ripped fine because I have been saving all logs and compiling them into a single large file.
So I will rip a group of cds and then the next day some of them will be missing, and it is allways a group of cds for example I will rip 20 cds and there will be a group of say 4 out of five that will be gone the next day.
So I tested and tested and worked out the issue I think.
Basically when you rip a cd and don;t close the ripping dialouge and then insert a new cd it will automatically start ripping, I use two drives though so that I can edit tags while the first cd drive is ripping, so anyway what I have found is that if you do this media center doesn't accept the changes you have made.
So here is a scenario where this might occur I start ripping say ten cds and of those ten, one is not found so i edit the tags and expect that that cd has been placed into d:\media\band\album instead it is still placed into d:\media\unkown\unknown and then I might go another 5 cds that are found until I hit another unknown cd so I enter the tags, but they also are not respected, so it gets placed into unknown as well, but get this it then overwrites the previously missplaced files. It does this even though overwrite files is deselected in options.
I am almost done ripping my cds so this is really a non issue at this point but it has been a pain in the past as I have reripped a few cds like 4 times and they would always just vanish the next day.