I would need an example to check for you, and if you could also let me know what browser you are using. We can then take a look. It shouldnt be leading to an incorrect location, so if thats the case its likely a bug
There is no way in which you would be able to prevent this at present unless you switch of items like about me, and use only items that use regular expression. You would then, in theory, write a regular expression to prevent these
I think to avoid confusion here, please can you screenshot what you are seeing as guest, and what you are seeing when logged in, then I can advise accordingly
-200 is an error returned from plupload on upload to the server, and is a server side error. You would need to check your server error logs to see what the actual error is there