"Glazing" usually happens from heat, not inactivity, BUT what might be happening is surface rust on the inner area of the brake drum. I suspect that if the brakes might initially grab on the first few stops, it's that surface rust which is being worn off. After it's worn down or smoothed out, then things work smoothly again.
One "allegedly bad thing" about riveted brake linings is that in extreme situations, plus some lower-quality friction materials (in some cases), I found some pictures where the lining material had broken around the rivets and then disappeared, leaving one or more of the rivets dangling from the brake shoe. Whereas the bonded linings were solidly-glued to the brake shoe, to better dissipate the heat and such . . . or so it was claimed. Back then, GM used riveted linings exclusively at OEM, so if bonded linings were ultimately better, but a slight bit more expensive, then Chrysler went the additional "mile" with the bonded linings. Plus, almost all GM linings back then had a groove down the middle, decreasing total lining area, but the bonded linings usually did not. Several things at play here.
If a lining might get hard with age, the usual result is more brake pedal pressure needed to stop the car, not grabbing and such. Which is why I suspect the inner brake drum finish, especially in a more humid environment. The other thing is that if you have been driving a power disc brake car and then get into a power drum brake car, you have to be cautious the first few brake applications, even in the ddriveway, so you don't "eat steering wheel".
Just my observations and experiences,
CBODY67