Karaoke midi files use the "@KMIDI KARAOKE FILE" text event to identify themselves. abc2midi places this event on track 0. TiMidity++ 2.13.2 unfortunately tests for this event only on track 1[0], which leads to the entire text being displayed before playing[1]. While I submitted a patch upstream to timidity, I doubt a new version would be released anytime soon (if ever). If abc2midi would place this event on track 1 (in addition/instead of) track 0, I don't think other programs would break, and timidity users would have a better experience.
[0] http://timidity.cvs.sourceforge.net/timidity/timidity/timidity/readmidi.c?revision=1.102&view=markup lines 471 and 5340.