if you make a redstone contraption like this whit a music disk C418 - wait in it. the repeaters blink on and off but the comparators don't unless you give them an update when the redstone turns on. also when you right click the comparator in front of the jukebox 2 times when the disc is inside the 3 comparators will stay on.

Note that this can be reproduced with any power source in place of the jukebox. Destroying and replacing the comparators (near the repeaters in the pictured setup) will sometimes cause them to remain active, depending on the timing of the placement.