No matter where I’m pasting into the decal goes to the workspace. I haven’t found any other objects that do this and I think it’s always been this way.
Yeah. It does that for me, too. Studio mistakes it as if you want to use the stupid cursor to place the decal onto a surface of a brick. 
I just decided to create a quick plugin to do it for me.
As far as I know it used to work but tried it about 2 months ago and it did as you said. I was sure I have used it to copy/paste decals or cut/paste them from the Part I accidentally placed it on and place it on the Part I intended to.