Ever test the weight of your chemical containers?

So following Waterbear's advice (given on another thread), I stopped by the nearby pool store to buy 4lbs of stabilizer. The shelf that had the stabilizer had a hand-written sign that said that if I brought back my container, I'd get a $2 refund (meaning, of course, that they've jacked up the price of the stabilzer $2 to motivate customers to return their containers). The price of the 4lbs of stabilzer was $14. I figured, then, that they probably refill those containers manually using a bulk supply in the back of the store.

As I returned home, I thought that the container felt a little light for being a 4lbs container. So, once I got home, I got out our electronic postage scale and weighed the container. It weighed just 3lbs 10.6oz! After I dumped the contents into my pool, I re-weighed the container to see how heavy the container itself was: 3.7oz. So, I was actually gyped about a half-pound of stabilizer, which works out to about $2 worth of stabilzer.

I'll bring this to their attention tomorrow when I take my water to be tested (perhaps for the last time at that store). But I wondered: Has anyone else found the net weight printed on a container of pool chemicals to be much greater than the amount of chemicals actually inside that container?