The cause of your problem, like so many that we women face, is probably gravity. What you’re seeing is not flaking, which is a common problem when the polymers that form a film around your eyelashes breaks down and flakes off onto your cheeks. It’s also not the same as smudging, which is, well, usually your own fault. You rub your eyes and move the mascara from on your lashes to…not on them.
This is more likely an example of migration; you didn’t touch it, it’s not breaking off in pieces, it’s just slowly, slowly slipping off the lash and onto your skin. If you’re fond of volumizing types, you might notice that raccoon look a little more, because these mascaras are heavy and weigh the lashes down.
Your best bet for prevention is probably to use less product. Stick to one or two coats max. This way, your lashes will be weighed down less. Plus, mascara is cohesive at one or two coats, meaning it sticks well to the lashes, but the more you layer, the less the mascara can hold itself in place. If that doesn’t help—or if you just can’t stop yourself from building for a dramatic effect—try a good waterproof formula and see if that does the trick.
Otherwise, try to enjoy the perfectly imperfect smoky-smudgy look and rock it like you meant it.