Thanks for all the remarks, everybody. I don't know if anyone remembers my post a couple of years ago about the dilemma I was having spending a $500 group birthday gift on bicycle accessories. I spent a lot of time shopping for panniers (including Ortliebs), LED lights, and other items, then threw in the towel and decided to instead put the money toward a neighborhood concert/party I am still planning. To appease all those who gave me the gift, I went out and bought a killer $5 32-LED flashlight, a $10 Schwinn frame pump, and this $25 Schwinn rack trunk/pannier. Surprisingly, all these items turned out to be more than sufficient for commuting and light touring, and I went on to brag about my cheapo finds on this and other bike forums.
I've certainly been around bicycles long enough to understand the difference between good stuff and total garbage, so I knew I wasn't buying a bag that was going to last years and years. But I figured whoever had the b-lls to purchase the Schwinn name would, at least, have enough pride to either put out a fairly decent product OR back it up with some semblance of customer service.
Whatever. There's no big loss here, and I can still use the bag to its standard capacity. When I tour again next year, I'll worry about expanding it or buying something else.