I have configured two languages: English (UK) and Ukrainian.
Then at some moment (no idea when) the 3rd language - English (US) - appeared in the popup and so I can switch to it by Ctrl+Shift
despite I haven't added it and in Control Panel / Language Settings I still have only 2 languages. If I add English (US) manually in Language Setting and then remove it, English (US) disappears from popup for some time, then appears again.
Looks like a Windows bug or some app is messing with Windows language settings.
Same problem on my work PC except I have only one language - English (UK) - there. So I keep switching to English (US) accidentally which is very annoying.
I'm sure I didn't have this problem on Windows 8.