Is emms-cache-sync really working without problems?

Hi,

first of all, thanks for EMMS. It is a wonderful piece of software.

I have the following problem: if I add new songs or tag old ones with 
Picard, emms-cache-sync does not update the cache. Even not if I do C-u 
emms-cache-sync. In some cases it is even worse: the updated albums 
disapparead from emms-cache-db.

I have to do: emms-cache-reset and then emms-add-directory-tree and then 
anything is working again... Except obviously one important aspect: I 
loose all the data about when I last played song X, song Y, etc. And I 
am very happy using filters with emms-browser-filter-only-recent...

Am I maybe doing something wrong?

Many thanks in advance!