Trev, first of all, I agree with your view of mechanical and the no worry of this and that.
Second I laughed when I had to look up zfg
But thirdly, I still think it's worth putting in some spacer when boxing a bike for a flight, especially with drop bars and like the situation I described, where the bars probably shifted in transit and the front brake lever got pushed vey hard, pushing the front piston out on my bb7.
The only thing I can think of is that the steel retaining C ring on the moving shoe of your caliper is worn/lost tension out so the shoe can drop out of the piston. It can't be pushed out by the operation of the brakes. It can be pushed out if you use maximum adjustment on the outboard adjuster. I just tried mine and I needed to lever it out with a screw driver, there was no way it could pop out under it's own steam.. The retaining ring is a little C ring on the shoe shaft. Because the shoe on the BB7 needs to pivot to compensate for the off centre pressure the BB7 creates it has a lot of slop and it's retained by the C ring. Technically the pad separating spring should also hold the pad and shoe in place. With the pads in place and adjusted to fit a disc there isn't enough room for the shoe come out. Potentially with a missing inboard pad and the outboard pads adjusted to the max it could come loose.
Anyway, it's a good chance to service your caliper while you have a look. It'd be worth trying to spread the C ring to add a little tension. They come with bugger all grease from the factory anyway, so a touch of high temperature brake grease wouldn't hurt to extend it's life.. The SRAM site has a service manual.