This and numerous other incredibly frustrating bugs have driven me nuts since the new 5.1 "update", and Apple's been playing games with this, as well. I called after a couple days, was able to speak to a higher-level tech person, and he assured me they were well aware of the mess, and promised a fix "ASAP". Well, 10 days later and no fix, so I called again, & spoke to a different higher-level tech guy. He tried to tell me the first guy wasn't correct, that nothing was wrong with Safari, and I simply need to disable/remove all my add-ons & extensions.
Well, that's a royal pain, doing that, then loading one at a time, opening & closing & checking Safari each & every time, and asked him if he knew WHICH ONES were causing the most problems, as it would be quite easy for them to check them out, & then inform us, their customers, which ones to delete (at least the most popular ones)....
He also said he's received no calls about people having problems, so either no one posting to this board, or anyone else experiencing problems have bothered to call or send Apple feedback, or he's just lying to me. I wish Apple would realize there's bugs in Safari, and just fix it already! Being distracted & lied to is no way to build customer loyalty, and is a betrayal of all of us who've been Mac-users for many years....