Hello.
Yes, this is a recently-known behaviour with the new Rending simulation engine (Insight v4+) and the old way of laying out points from Lighting. We will be releasing a new addin and engine improvements shortly to address it.
What's happening is that the illuminance value for a grid point gathers the effects of light on the region of the point (up to halfway to the next point) rather than just at the analysis point like other ray-tracing engines. With low-density grids like the 24 in grids for sDA, this effect is highlighted for points near walls. For higher-density analyses like 'Illuminance', where the simulation grid is more dense and is then sampled down for display, this effect is removed.
The improvements about to be released will do 2 things: Focus light gathering closer to the point, and remove points very close to the edges of Floors and/or Rooms (with an optional user-setting for the buffer).
Another thing to keep in mind is that for the 3D views, results are projected onto the Floor elements, and with a surface Analysis Display Style, the colors are interpolated between points, so it may appear that light is shared across a wall, but this is just a display artifact. If you look at a '...pts_anno' style, you can see the actual points values. This effect is not seen in Plan views, as the results are projected on Room elements, which bound the interpolation to Room boundaries/Walls.
David