In trying to just "Reply to this topic," I find I am unable to do simple copy-cut-paste operations in the window as I'm typing in text, with the usual Ctrl-c, Ctrl-x, Ctrl-v.
Actually, as I'm doing the same thing to try and post this comment, I now discover that I can somewhat inconsistently Cut some text with Ctrl-x, but it has yet to ever paste that text back in with a Ctrl-v no matter how often I try.
The little icons at the top of the text window which have Copy, Paste, Paste as Plain Text, and Paste from Word occasionally pop up a warning window asking if I want to allow the browser access to my computer's clipboard (which I'm not necessarily worried about, just puzzled it ever gets to that extreme).
Let me guess... You're using Internet Explorer?
I did a bit of research into this and I'm afraid I have to punt on it for the time being.
Microsoft, in their infinite wisdom, wrote something into IE11 that breaks Tiny MCE, which is the text editor we use here on TD (along with half the friggin' internet).
Microsoft is the worst. The absolute worst.