Mix Question muted tracks appearing PT 10.3.7 Mac OS 10.7.5

Hi I have some tracks muted during mix down until later in the song when I un mute them. I mix down to 24 track stereo mix, and it sounds like what I wanted. Then I burn to Disc…and the mp3 doesn't reflect the same mix…the tracks that were muted are present all the way through. Im confused since they are muted, and the mix sounds good the way I want in the 24 bit wav mix…only after bouncing to disc does the mp3 not reflect the mix I had. Any HELP?