Strange disappearance

First yard waste pickup of the season today, and I had two trash cans full from cleaning the garden. However, one of them, along with its cargo of grass stems and sedum heads, has vanished from the back yard. I thought the landlord had put it by the curb, but it's nowhere in sight. It can't have rolled away in the wind - it was behind a concrete bumper, and the back yard is fenced. Nothing appealing in it for animals, and why would they take the can? And if a person took it, why take the contents - and why take the plastic can and not the metal one? And why now? Those cans have been sitting in the same spot, used for the same purpose, for years. I'll be checking the neighbors' places out on the way home, but it is most peculiar.