It looks like nobody is going to fix the bug, so this is what a new user should do to create a new account:
locate the file captcha.js and edit line #18 as explained here,
save captcha.js and reload the webpage, forcing the new captcha.js to load. On Chrome, and all Chromium-based browsers, this can be done in two ways:
> saving captcha.js locally (best way, IMO), or
> setting a breakpoint before line #18, reloading the webpage and then editing captcha.js (to set a breakpoint you just have to click the line number).