Sometimes, for no good reason, the keyboard layout changes on me. I've yet to find a pattern, but as another user reported, I often notice it at login when I type my password (I think that at those times it just had changed before shutdown an I didn't notice until login).
But now, the oddest thing about this bug is what you can see in this screen:
I have both US and PT language set to use the PT keyboard layout, but at times it changes randomly and without my intervention to US with US layout, when that isn't even an option I have enabled in the preferences... but then I can cycle though it using Win+Space, really odd.
I've yet to figure what triggers this bug, but I hope this information is helpful. (maybe some "default" is triggered somewhere)