I am not familiar with wireshark/tcpdump, but I will look into it. For me this issue is both intermittent and illogical in the way it shows up. Sometimes Cookie will work exactly as expected for several days, then suddenly start acting up again. Very frustrating. Since the makers of Cookie know that their product has to work with Safari, which works with iCloud, you'd think they would have anticipated this issue. What's the point of a product that deletes browser history if you have delete it manually anyway? What's the point of a product that saves your favorite cookies, but only sometimes? This is the first time I have mentioned this last issue, and I will start a separate thread on this subject at some point.

I agree that Handoff is a likely suspect, but Handoff is not enabled on my Mac or on any of my mobile devices.

Yes, it may be that iCloud is re-syncing Safari's browsing history with mobile devices even after the user has cleared history and website data on those devices. Clearly, this should not be happening. Whatever the cause, the fact that this behavior happens intermittently makes it even harder to investigate. Sending a bug report to Apple probably won't help, but it can't hurt.

Followup: The problem I described is definitely not related to syncing of browser history with iPhone or iPad. I quit and launched Safari less than an hour ago and the browser history was clear. After visiting a few sites, I quit Safari again and went out. When I opened Safari just now, hundreds of entries from yesterday's history (and earlier today) have magically reappeared. I have not opened Safari on my other devices since I cleared their browser history yesterday. The behavior I described in my original post is definitely a bug.

Extremely unlikely because I rarely browse the web on my iPhone and iPad. When my history reappears, it is always several consecutive days worth of history with many websites visited each day. Just to be sure, I have just cleared the Safari history on both iPhone and iPad and will see if the problem recurs on my Mac. Stay tuned. Thanks for your reply.

My Cookie preferences are set to delete my browser history when I quit Safari. Normally this works as expected; but once in awhile, I will discover that my browsing history for the past several days has mysteriously reappeared. This should be impossible since I always quit Safari before putting my computer to sleep each night. It is conceivable that I might forget to quit Safari once in a great while, but not for several days in a row. The reappearance of my browser history must be the result of a bug in the Cookie app. Is there any place (besides this forum) where I can submit bug reports pertaining to my use of Cookie? Has anyone else experienced this issue?