I'm treating this as a duplicate of your other post Silent data loss when saving recurring WWW/MP3 or certain/WMA tags which is basically on the same topic (here the data is already there and vanishes on write, there you enter the data and it disappears on write).
The slight difference is probably the change of the description text to uppercase, which you haven't mentioned in this post and which I'm treating as not a bug (as already mentioned elsewhere as a reply to one of your other posts).