Hi there, and welcome to the forum.
I am not sure why XBMC is not picking up the tags, is there any posibility that it is skin related. I know that some older skins used a hack to display the media tags that were all located within the studio tag.
I use the Transparency skin and it works perfectly.
Finally, if all else fails, you can disable the media tags in the preferences. XBMC is now capable of getting these tags directly from the media.