I am a big fan of keyboard commands.that's why i use ctrl+d, ctrl+shift+d, ctrl+e ctrl+shift +e etc, very often.It worked great in 7.0.
Since I use 8.1, I experienced some problems.
If the base point is out of the object (wall, object, stair) that I want to move. copy etc., the object will deselect automatically. If the base point is on the object, wall, slab, then the commands work.
This doesn't happen always, but quite often and it's very annoying.
If I restart the program everything works again.
Is it a bug ?
I experienced this problem both on a commerical version as well as on a edu version.