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New update. I found if you go into the commands associated with the keyboard when you turn it on and inactivate the space bar command (choose clear) then things work ok. I have the accessibility turned on now, facebook is working and now I have no problems typing here or other websites. A fix for now hopefully the deactivation of the space bar in accessibility on for keyboard will not cause other problems but in general this now seems to be a solid fix. Who know when 15.2 comes out
Thanks, that seems to work when editing comments on facebook which were playing up after turning on the keyboard full access in Accessibility. It shouldn’t be this hard to use the magic keyboard though, so hope they fix it soon.
 
As the OP, this problem appears to be related to another problem I was having using the keyboard and typing in my browser’s search bar. Whenever I hit the space bar, the curser would jump out of the search bar and the search would begin based on whatever I already had typed. The new OS update and eliminating a spacebar command option under Accessibility>Keyboards>Full Keyboard Access.
 
You need to go to Settings -> Accessibility-> Full keyboard access, then turn it back ON. It seems the upgrade to 15.1 turned it OFF and leads to issues with the Magic Keyboard.
 
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