First, it is an issue raised only with the AA HS hulls(all gauges). These hulls have a tube, basewad, and brasshead construction. If I understood the problem, it had more to do with priming these hulls in machines like my P-W's where the rim is held while the primer is forced up into the pocket (as Jon touched on). Apparently, this can, on occasion, dislodge the basewad, since it is only being retained by the rim crimp.
I have yet to load any AA HS hulls but have many in small gauges. I think I'll section some in various gauges to see how they differ from other makes that have separate basewads. The separate basewad is not a new thing. I believe many Federal and possibly even the .410 (only) STS hull may be a tube/basewad type construction.
I think it's more likely that this is a problem particular to Winchester's execution of the three piece hull design.
