copy/paste of nodes only works first time you do it

The first time you select some nodes and hit Ctrl+C to copy them, it works, and you can paste those nodes as many times as you want. But if you try to copy some different nodes into the clipboard (using Ctrl+C a second time), it doesn't work... it still continues to paste the first group of nodes that you copied earlier.

Only way to get it to quit pasting the old nodes, and let you copy/paste a different group of nodes, is you have to shut down Unity and restart it. Then you can copy/paste a different group of nodes. But again, it'll let you paste them as many times as you want, but it'll only let you copy once.