Why is Silent alarm now ringing?

[iMore Question]

I bought a silent ringtone for my iPhone 6 through the iTunes app. It worked great at first; I could set an alarm and the phone would only vibrate, not ring. But then the "silent" ringtone suddenly started to ring audibly ("radar"). Though it might reset things if I changed the selected ringtone to an audible tone, then back to the silent ringtone, but that didn't help. Restarting the phone (regular way, and forced reset way with home and power button simultaneously) also didn't fix it. Deleting the alarm and recreating it didn't fix it. Then the iOS 9.1 update came along, and when I installed it my silent ringtone went back to silent. But now it's started audibly ringing again. Very annoying. Any ideas?