There's a character in Orson Scott Card's novel Pathfinder who is able to go invisible by travelling forward in time in tiny intervals (i.e. she goes 5 nanoseconds into the future, stays for 1 nanosecond, and goes 5 forward again, thus making her imperceptible to sight and making her perception of time as travelling at six times the normal rate).
When an object passes through her while in this state, it often leaves severe burns from radiation or whatever. She also uses this ability to walk through walls, provided the material is not too dense.
My question is: if Param can walk through walls like this, what is to prevent her from falling through the floor and into the ground while in this state? Orson Scott Card normally thinks things through more thoroughly than to leave a plot hole like that, so I think I'm missing something.