I've run into this issue. The research I've found leads me to believe that there is somewhat of differing standards concerning lyrics. There's the simple text meta code, there's the lyric code, and some variants of text for differing purposes. Some of these you won't even see in Sonar because Sonar's default behavior is to hide all midi events that occur before 1:01:00.
I'll take a guess and suppose it's Yamah's XF standard they're following, requiring a note with the lyric - but
don't quote me on it - I'm just guessing.
Some midi player's just don't care, and will play lyrics whether they're text codes, lyric codes, with a note or not, and will even play .kar files. As I said, I haven't pieced it all together yet. I'm sure this behavior has been around for quite some time - it would take a long-time baker to answer the reasoning behind it.