Steps to reproduce:   

1) start a NoMachine virtual desktop from Windows (or a physical desktop session)
2) open a terminal in that session  (e.g. xfce4-terminal)
3) give focus to Windows, outside of the NoMachine session window and copy some text from a Windows application, by using Ctrl-C
4) give focus to NoMachine session again (with Alt-Tab sequence or just click in the NoMachine desktop), and inside the session give focus to the terminal
5) press Right-Ctrl + Shift + V to paste the text you copied from Windows to the terminal: your Control key is toggled on.

A similar problem occurs also when sending to terminal Right-Ctrl-C. Note that only press Right-Ctrl does not trigger the problem. You must press Right-Ctrl plus another character to reproduce and Right-Ctrl has to be the first key to be pressed after giving the focus to the NoMachine window.

The Ctrl key can be unlocked (toggled off) by:
- giving focus to Windows
- giving focus back to NoMachine
- press any key other than right control

Typing is then normal again.

If the first key you press after giving control to the desktop is any key other than right-control + shift + v, you will not see this problem. Another workaround is to use left-control + shift + v to paste.