When I add characters that use an umlaut or other unusual character (unicode?) to the APETAG of a MPC, the full field isn't displayed in the playlist. It is displayed in MP3s, so it seems to be a xmms-musepack specific problem. The tags were manually set using the xmms-musepack apetag editor.
I'm using XMMS 1.2.10+cvs20050209-2 (Debian sarge) with xmms-musepack plugin 1.2 RC1.
A screenshot of the problem showing the full tag as output by the 'apetag' utility, and the "cut off" tag in the XMMS playlist:
here (edit: replaced with link for users with limited connection)