Same problem with Lubuntu 16.04 (it wasn't there before, in Lubuntu 15.04).
4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
Workaround with Ctrl+Alt+F1 and back, reported by [duro (dur0)] works for me too.
Same problem with Lubuntu 16.04 (it wasn't there before, in Lubuntu 15.04).
4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
Workaround with Ctrl+Alt+F1 and back, reported by [duro (dur0)] works for me too.