I have not heard of this happening before, however, with 6.1 came a second alarm. AlarmInfo only sets and checks Alarm1. If you have used Settings to set Alarm2, you will need to use settings to turn it off.
If this is not it, you will need to check with your phone network support group, or a good user forum, like
www.pdaPhoneHome.com.
Regards,
Rob.