MC13 uses ID3 V2.4.0 to store mp3 tags.
MC13 stores a database 'list' field as a TXXX mp3 frame using
semicolon as a separator between each term of the list.
On the other hand, some players such as Foobar (Windows) or Quod Libet (Linux) store 'list' field as TXXX frame using
null as a separator between each term of the list.
As a result these players interpret a list tagged by MC13 as a single term. On the other side, MC13 reads only the first term of a list tagged by these players
http://www.id3.org/id3v2.4.0-frames says:
§ 4.2 [...] All text information frames supports multiple strings, stored as a null separated list, where null is represented by the termination code for the character encoding".
TXXX being a (user) text information frame (described inside § 4.2 chapter) we can think the above rule applies to TXXX also.
So it seems to me that MC13 doesn't implement 'list' tag according to the standard, preventing others players to recognize it as a list, only as a string.NB. I know MC list is described as "semicolon delimited" but I think that comes from previous version of MC which did not have a list editor so you had to set a string "semicolon delimited". Anyway, whatever the reason, MC should comply with the standard.