On Ubuntu Mate 16.04, on my Lenovo Yoga 510-15ISK laptop, today, ALT+TAB broke, like it has before every few weeks or months or once a year in the 2010's, the past few years, at times, randomly, maybe a few times a year, randomly. So, that means, I couldn't use some of the keyboard shortcuts to switch between windows and a few other things. I was able to switch between Firefox tabs but was not able to switches between different work spaces. Before, I would restart my computer to fix this disability, this error, this bug, or whatever it might have been. Today, I was trying to figure it out again and press F9 which has a lock icon on it, and that unlocked the switching shortcuts, etc. Interesting. 2018-09-12 Wednesday 08:35 PM LMS JA Oatmeal Joey Arnold L4OJ PST.