I was wondering how common this is. I'm going to be in Yosemite Monday on a four day hike and this is the first time using a bear canister. They say to keep it 100 yards from camp, and I'm fairly certain that's far enough away that someone could come in, spark their stove, and eat my food without me knowing any better.

Hopefully the people backpacking in Yosemite are of a better sort than you encountered.