I'm wondering if this is because I use LockInfo on my JB'd iPhone 6 (iOS 8.4). If I set up a recurring weekly Reminder, at due time it pops up on my Mac and iPhone. If I mark it complete on the Mac and then, later, look at my iPhone, see the Reminder, slide it left and mark it complete, what happens is the next occurrence also gets marked as complete. The next Reminder ends up being for 2 weeks out. Does this happen on a stock iPhone also?