Default Unable to Shut Off Default Calendar Notifications

OK, this is a bit minor, but it is really bugging me. I use Business Calendar Pro for my calendar. I turn on notification with Business Calendar, and then turn them off in the Android calendar. That way I won't get two notifications. This has worked with the past three HTC phones.

The problem is that no matter what I do, I can't get the built in calendar to stop posting reminders. Every time a reminder goes off, I get two notifications. I've gone into the default calendar app and made sure the notifications are off, but when I get a reminder, it appears that the setting gets turned back on. This is not one of the apps that can be disabled either.

I've also gone in and deselected all calendars from the app, so that it should not in theory contain any appointments anyway.

I'm not rooted, but I'm hoping someone else has had this and found an answer.
Phone: HTC One M8 T-Mobile, Stock ROM KitKat
Tablets: Lenovo IdeaPad A2019 9" Tablet / ICS | Dell Venue 7" Tablet / JB
Laptop: Toshiba Satellite T925u / Windows 8.1
Former Phones: Ericsson T-28, Ericsson R600 World, T-Mobile Windows Phone, HP 6310, Sony-Ericsson M600, HTC Pharos, Asus P527, HTC Tilt2, HTC HD2, HTC Amaze, HTC M7