This has to do with the surface tension of water. That surface tension causes the drop of water to retain its shape, preventing it from going through the tiny pores of the membrane. But as the surface tension decreases, the droplet loses its shape and can indeed penetrate the pores of the membrane. After all, the material still features tiny holes.
It may also be that the membrane is damaged from the inside.
Damage to the interior of the toe boxes could be caused by toe nails that are too long, for example.