I experience similar but only with the contrast keys, which get deactivated at some point during a session. At first they work, then suddenly they produce a darkened contrast (sunset symbol icon) with a circle and a diagonal line crossing through it (like a stop sign or no entry sign) in black below it which pops up on the screen when i press a contrast key. Restarting my Macbook fixes it for a while, but the problem always returns. I like to use the contrast keys because my Macbook Air (being non retina), does make my eyes blurry after a few days consecutive use. I have to then return to use iMac for some days when that happens because the truth is, non retina screens on Macbooks are very very bad for my eyes with prolonged use. Also i get electric current in my hand and skin peels off my fingers from the trackpad and slim blade like front edge in front of the trackpad, and have a stucky plaster on the front edge and have to wear a plaster on my thumb too to avoid scarring. There seems to be some kind of damaging currrent or wireless waves which are passed into my hands when using the macbook air. Currently wishing to sell both of my Macbook Airs (11 and 13 Inch), because i have found during the last 3 years that they damage both my hands and my eyes. Still waiting for Apple to make touchscreen Macbooks, as the iPad i have doesnt work for true desktop style browsing and editing my websites, the safari browser and others just refresh page all the time when editing, and wont allow me to use things like tiny mce text editors in my online store product editors etc, so the only way to webmaster is in a desktop browser. We need a mac thats a tablet Mac.. but Apple seem to be too focused on selling multiple devices than to integrate touchscreen into a fully functional Mac
