When you drag a 3D object in Plan view (Layout window), as soon as you move the mouse over a wall, the furniture automatically aligns to the wall so that you can just click the left mouse button to release it.
Sometimes such behavior is not needed (or even unwanted): in this case press the SPACE keyboard button: you will disable the automatic rotation. Press it once more to enable it again.
This article is valid for DomuS3D® 2017 and later versions