Ubuntu – Ctrl modifier key not working

I have just installed a fresh new Ubuntu Gnome 16.04 and am having a weird problem.

The left and right Ctrl keys are not working as modifiers. I can see them both doing what they should in xev but if I try and do a Ctrl+L to clear my terminal or a Ctrl+A in a document to select all or any other key combo involving Ctrl it will not do anything.

I have looked through accesibility/universal access and keyboard settings to see if I can see anything obvious but I cannot and am completely stumped. Any ideas??

It appears when I press Ctrl in a terminal with a second key, Ctrl+l for example, the terminal titlebar flashes in the same way it does if you press the down arrow when you are already at the bottom. Not sure if this is any help in diagnosing my issue or not??

I have tried using copy/cut/paste shortcuts in gedit and they don't have any noticeable effect.

Output of xev when I press the Ctrl keys

KeyPress event, serial 34, synthetic NO, window 0x13e00001,
    root 0x2d3, subw 0x0, time 192257122, (75,49), root:(75,75),
    state 0x10, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x13e00001,
    root 0x2d3, subw 0x0, time 192257222, (75,49), root:(75,75),
    state 0x14, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyPress event, serial 37, synthetic NO, window 0x13e00001,
    root 0x2d3, subw 0x0, time 192263578, (75,49), root:(75,75),
    state 0x10, keycode 105 (keysym 0xffe4, Control_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x13e00001,
    root 0x2d3, subw 0x0, time 192263658, (75,49), root:(75,75),
    state 0x14, keycode 105 (keysym 0xffe4, Control_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

Interestingly the above is the result of two single keystrokes (one each left then right) is it normal to have two events per keystroke?

I have accidentally discovered that when I cut/copy/paste keyboard shortcuts do not work in either, Ctrl and scroll wheel still zooms in both libre office and chrome browser

UPDATE

I have stumbled across a fix. In the 'Keyboard and mouse' tab of gnome-tweak-tool. I enabled 'Show All Input Sources' and 'Show location of Pointer' and as if by magic Ctrl is behaving as expected. Weird.