I'm not sure what you mean. As far as I know, it works normally. Here's a screencap, where I've copied some text from LoTRO mail, and pasted it into Notepad:
Are you using a Mac? If so, then it may just not work. Some features that work in the Windows client don't work in the Mac client.
If you're using Windows, it's the same procedure as always:
- Select the text.
- Press Ctrl+C to copy the text to the clipboard.
- Go to another application (Alt+Tab).
- Press Ctrl+V to paste the text from the clipboard.