Ask HN: Captcha When Changing Google Settings?

One of the things I have always done with Google Search is to change the "results per page" to 100, as I find the default of 10 per page to be tedious.

However, lately, Google has been giving me a Captcha every time I try to change it to 100. It does it to me at work and at home - and it does it to me in Chrome, Firefox, and Safari. I find this quite annoying as my regular browser is set to remove all cookies on quit.

Does anyone know if this is some kind of programming error? My first though was that Google is trying to punish people who frequently clear out their cookies to avoid tracking but then I remembered Hanlon's razor.