Looks like a bug when using SF on Windows. Will look into this for Beta 0.16!

I have now had it confirmed from other testers, it's a Windows issue!

That could (But shouldn't) be the cause of you not being able to delete connections

That's very strange... I'll have to try it on my Windows machine later at home

Are you selecting nodes, and then holding ctrl and then press D when attempting to duplicate?
Are you hovering the cursor over a connection when you press delete, to remove its connection?

No idea, it's very strange. Is there anyone else having similar issues?

I've only tried it on OSX, but everything works perfectly fine for me. I assume you've tried restarting Unity? Also, did you delete 0.14 before installing 0.15?