I purchased a 6 month UFP on August 31, 2017 that expires on Feb 28 2018. When I tried to renew the pass today for a further 6 months the new expiry date showed up as August 28, 2018. My simple math tells me that 6 months plus 6 months equals 12 months (August 31st 2018), but to Air Canada it appears to mean 362 days.

Here is the wording on the flight pass:
"Valid for 6 consecutive months from date of purchase. Travel must be booked and completed within the validity period. No extensions will be permitted. It will expire at 11:59 pm (GMT) 6 months after its purchase date. Please make the necessary adjustments for your local time zone."

Not sure they thought through what a "consecutive month" means. I suspect it only makes a difference for a 6 month UFP purchased August 29-31 or a 3 month UFP purchased on November 29-30.

Oh, and I just noticed the bit about the FP expiring at 11:59pm GMT. That would mean that my current FP should expire at 6:59pm EST on Feb 28th. I just checked and I could book a flight at 9:00pm on Feb 28th, so I guess the folks that programmed the FP rules missed that last sentence"