Every once in a while I want to post a question or an answer and the controls are missing and the preview area never populates. In fact, this is happening to me with this question right now. Here's a screenshot:
If I submit a post when this happens, I get the "Human Verification" dialog with a captcha; normally I don't get that.
Reloading the page doesn't fix the problem. What causes this and how can I fix it?
Addendum: Loading the initial article page (Is this rule for graph isomorphism true? in this case) produces the following diagnostics on the JS console:
* The connection to wss://qa.sockets.stackexchange.com/ was interrupted while the page was loading. full.en.js:1 "soup injecting fixes" SOUP.user.js:1158 "soup init complete" 950257:29 "soup setup complete" 950257:29 "soup mathjax config loading" 950257:29 "soup adding vote event handler for mse115702" 950257:29 "soup JS fixes applied" 950257:29 * no element found a930:1 * TypeError: SE.mathjaxEditingNew is undefined mathjaxMSEincremental.user.js:773 Use of getPreventDefault() is deprecated. Use defaultPrevented instead.
Items with stars are errors.
On the other hand, this page shows the same problem for me just now, and the console doesn't show any of those errors, so I'm not sure the errors are related.
Added 20141010: The problem was caused by an obsolete GreaseMonkey script. This bug report can be closed.