Receive Shadow Mesh Renderer - Weird Effect

Hi everyone!

I have a very simple case. A scene containing different cubes rotated by 45 degrees on the Y axis. If the "receive shadow" flag is set to true in the inspector for the Mesh Renderer of the cubes I noticed this weird edges:

In the image we see 2streched cubes side by side. The right cube generates shadows on the left one, BUT it also has a weird edge with white spots (is it aliasing?).

However if I set the "receive shadow" flag to false I get:

No weird effect on the edge, but also no shadows (obviously).

Since I wanted to maintain the shadows in my game, is there a way to get rid of this strange effect on the edges? And if someone also knows why this happens it would be nice to have an explaination, since I would like to understand why this happens.

Thanks a lot for any answer :).

Note: this happens with the default material (and also others that I tried out).