As far as I can tell, I haven't seen anyone mention this issue, so forgive me if it's already a known bug with the CE builds.
It would seem that sliders love to screw around with custom comboburst sounds, as it seems to me that whenever I hit my custom milestones on sliders it will occasionally eat the trigger, and the sound won't play whereas I've not yet seen it fail to play on normal circles. Sometimes it'll play if the milestone is on the slider end, but slider ticks always block it, and I've yet to hit the milestone on a slider start.
If I manage to fix OBS, I'll post a video or some such for proof, but should you want/desire my skin file for testing I can provide that now as well. Until then, I'll continue experimenting with it.
(Yes, I'm certain that I skinned the files right, because they've all played at least once.)