The tape is playing but ignore the end of tape time.
Indeed, I just see that the line of code that would bring the cassette data into the machine is commented (I don't know why, that seems correct to me):
http://git.redump.net/cgit.cgi/mess/tree/src/mess/drivers/mc1000.c#n326// data &= (((cassette_input(state->cassette) < +0.0) << 7) | 0x7f);
(The sound of the cassette becomes 0 or 1, and becomes the most signifying bit of the byte that is served by the selected port.)
