Never heard that term zipper blow out. I know I ran into some nice folks who had a 2001 diesal pusher, forgot what model A/S that is. They blew the left front on their way to Jackson Center for other work. It did cause some damage and after arriving at Jackson Center they took their pickup (which they were towing) and headed for a Michelin dealer in Dayton.
The folks told me, like you that they had checked the tires and they were running proper inflation all around. After inspecting the tire, the dealer told them that he felt it was a failure of the tire that it should be covered by warranty. He then called Michelin and they informed him that they would not cover the tire unless it was shipped to them (at the owner's expense) for analysis. If they felt it was underinflation, the owner would not be reimbursed for the tire or the shipping charges.
The tire dealer appolgized to the owners telling them that he had to follow Michelin's instructions even though he felt strongly that he should have been allowed to replace the tire based on his inspection.
The owners felt let down since they felt that Michelin should have allowed the local dealer to make the replacement determination. Especially considering the expense in shipping the tire to some national center.
Bottom line, I get my weight hat back on, have you ever weighed your Cutter on a per wheel basis? There always is the possibility that you could be in an overload situation even though your air pressure was within normal specs and potentially your axle was within weight limits.
I also remember at a seminar about tires that there are warnings regarding tire capacities. Some of the info we were given stated that a tire mounted in a dual situation has less capacity that if it used in a single mode. Most tire rating charts note the differnce in single vs dual load capacities for their tires. This normally should not be a problem since you do have two tires carrying weight, unless you get into a situation where in leveling, one tire of the dual wheel ends up carrying the weight. If this happens you can damage the tire belts. They noted that any leveling blocks or other materials placed under the rear wheels should equally support both tires on a dual wheel. Another issue they brought up was that the inside tire normally runs hotter in a dual tire situation. Any problems with under inflation are magnified since heat becomes that much worse.
Here is an article regarding tire loading. You might find it interesting.