Do Not Disturb turned on, call got through after being silenced 7 times

Hi all,

I scheduled DND to automatically turn on every night and it's been working fine until tonight. Someone called me during the night and after 7 missed (silenced) calls, the 8th got through. Fortunately I was not asleep yet but it was very irritating as I don't like being disturbed at night.

"Repeated calls" has always been and is still disabled; the 8 calls took place within 16 minutes and came from the same number, which was not in my favorite (it wasn't even in my contacts) so I really don't know what went wrong.

I was not using the phone at the time so I'm sure it was locked.

Has this happened to anyone else?

iOS 6.1.3

iPhone 4S

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