I recently had the same issues that others had of their keyboard space bar not working on CC replies along with other keys. I checked my usb keyboard and it works on other computers fine, so I looked at my browser which I updated a few days ago and that's when I found the issue. I use Yandex browser ( a chrome/opera derivative) and when you update the browser it has adobe flash and java within the .exe install file and overwrites the old browsers adobe and java files.....The programmers however have not addressed this issue and there seems to be a bug where the adobe flash/java doesn't recognize the spacebar......

The solution that worked for me was to uninstall the browser (keep settings, bookmarks), restart the computer then reinstall my browser....and the spacebar bug is now gone....
it has to do with adobe flash/java having a bug that does not go away by simply updating the browser but by reinstalling it I think it clears the cache....hope this may help!

Steps:

1. uninstall the browser but save your bookmarks, passwords, settings and do a basic uninstall
2. restart your computer
3. reinstall the browser
4. try out on CC and the spacebar/other key letters should work.....