The email I got from sweetCaptcha 3 weeks ago failed to address the problem (the sweetCaptcha readme file clearly says that it doesn’t support WordPress 4.1), so I decided to switch to the CleanTalk anti-spam filter. During its free 14-day trial, I noticed how it works so much easier than sweetCaptcha and it requires no extra work for the end user. So I spent the extra $8 for a full year of coverage for my website, and I’m satisfied with the results.