This seems to be a known issue, and it has been stated by Robert Cupisz (a UT graphics programmer) that they plan to fix this in the near future. It can be compensated for in spotlights by adjusting those Bias settings, but not with point lights.
As a workaround, you can try individually unchecking "Cast Shadows" on the surfaces which show the artifacts, but this will of course mean that they won't cast shadows on objects behind. This is often fine for the floor, but not so convenient for walls, if they're supposed to cast shadows around the rest of the scene.
For more information, see Robert's reply to a similar question, here: