Sorry for disturbing you but even if I posted after some days digging into this problem appears wasn't enought as I finally found the solution and here it is for people encountering my same problem:

Some tag editors just edits last version of ID3 that appears if you had ID3V2.3.0 already set they doesn't replace it neither when you clean up all tags and N900 is looking for first valid ID3V2 datas.

To be more precise I had ID3V2.4.0 data updated while ID3V2.3.0 were old and what N900 was reading!