Hmmm. Seems odd. There should be plenty of velcro surface area to hold the spine end together.
Be aware there is a 'pocket/tunnel' between the sail fabric and 1st piece of Velcro sewed onto the sail. The spine extension slide through the tunnel and into the spine. Then the velcro 'tail' is flipped up and over, pulled taught, and pressed firmly against the mating Velcro strip.
The only time I've had this fail is once in big wind I should not have been flying in. Ken suggests tying the extra leech line ends around the extension to keep from losing it in the event the velcro does come loose.
There are some pics on Ken's site somewhere...
Seems Doug and I hit Save at the same time.