I can't add any new components. Looking at the console, there's a 500 error:
Failed to load resource: the server responded with a status of 500 (Internal Server Error)
hook_80191503.js:8789 Uncaught ReferenceError: responseText is not defined
at Object.onFailure (hook_80191503.js:8789)
at Object.wrapper.extend.$owner (hook_80191503.js:40)
at Object.onFailure (hook_80191503.js:8751)
at Object.<anonymous> (hook_80191503.js:42)
at Array.forEach (<anonymous>)
at Function.forEach (mootools-core.js:5)
at Array.each (hook_80191503.js:9)
at Object.fireEvent (hook_80191503.js:42)
at Object.wrapper.extend.$owner (hook_80191503.js:40)
at Object.onFailure (hook_80191503.js:134)
Never seen this before. It looks like a new bug to me. Can you take a look?