I'm assuming this is a rare bug because it's never happened to me before, yet it is still a bug so I'd appreciate if can be looked into. At around 03:27 server time, I got a security check. I'm using alternative SC mode. I answered the check immediately, and was prompted with the "You have successfully solved the captcha and increased the timer" or similar message. I let my auto run for a bit, then went to check the market. Upon my return and trying to start another auto, I got another SC. This was at 03:36 server time, so less than 10 minutes since I answered the last security check. My timer has built up to around an hour or maybe more at this point so this definitely shouldn't have happened.
As I said, seems to be a rare bug because it hasn't happened to me before, but it's a bug nevertheless, if I wanted SCs every 10 mins I'd use the regular SC mode.