http://ckeditor.com/demo is working on Android 5.1 - standard browser and chrome
I don't know if this has changed with 2.0 or has always been the case, but I'm currently using custom 403 and 404 error pages.
With pretty URLs enabled, if I go to non-valid URL, the URL that shows my 404 page becomes "mysite.com/the/full/path/to/my/site" which seems like a security concern to me
I rechecked how 404 is behaving in v2.0 and could find nothing amiss.
Perhaps your issue has got something to do with your local configuration?
Are you sure the highlighted line is uncommented and set properly in .htaccess (specifying sub-folder if required) -
#If you wish to use a custom 404 page, place a file named 404.php in your website's root and uncomment the line below.
#If your website is installed in a subfolder, change the line below to reflect the path to the subfolder.
#e.g. for http://www.example.com/subdomain1/subdomain2/ make it ErrorDocument 404 /subdomain1/subdomain2/404.php
#ErrorDocument 404 /404.php