It doesn’t look like just the sound, because during the first 10 minutes past the scheduled time there was nothing, not even the notification. I will further investigate it. Let’s see when it comes back.
Either way, along with some Calendar alarms also broken by 4.5.0.x update, this makes all SFOS alarms/reminders completely unreliable, and I am starting to wonder how can I continue to use this phone as my daily driver if I can never be sure not only if it wakes me up but also whether it reminds me about important events. Should I be carrying a second device for that purpose?