Unable to edit bookmarks after Chrome import

I signed up for the Yosemite public beta over the summer, and after I was accepted and completed my upgrade (PB 2 or 3, I believe), Safari asked me at first launch if I wanted to import my bookmarks and history from Google Chrome. I said yes, and everything seemed to work okay. Chrome was still my primary browser, but it was nice to have everything in Safari if I needed it.

On the Safari Home screen (Top Sites), there is a box at the bottom that says "The sites above include your bookmarks and history from Google Chrome" along with two options: Keep | Don't Keep ... I never really paid much attention to it until recently. But suffice it to say, the buttons do not work.

If I try to edit any existing bookmark, I get a separate dialog box saying much the same thing: I'm using bookmarks and history imported from Chrome, etc. etc., but in smaller type, underneath, it says "Safari imported these when you started using it on December 31, 4000, so you could try out Safari with your data." My three button options here are: Don't Keep | Cancel | Keep Data from Google Chrome. The only button that actually does anything is "Cancel". The others don't even get rid of the dialog box. These "options" appear every time I try to add a new bookmark or edit or delete an existing one. Since I can't remove the warning, I'm unable to complete any action.

I have searched high and low for a solution to this, but I'm apparently the only one to ever encounter it. I've tried just about every solution I've seen for issues that seem even potentially related: I've reinstalled OS X, I've turned off extensions, I've cleared all website history and data, I've deleted virtually every Safari-related file and folder I can see if ~/Library/Preferences, /Library/Caches/, and /Library/Safari. I've deleted .plist files and .db files. I've deleted all extension-related files. Nothing has worked.

The fact that the warning dialog references "December 31, 4000" clearly suggests something went horribly wrong somewhere. But I don't have the first idea where it could have been and even less of an idea of how I might go about fixing it. If anybody has any suggestions or solutions, I would be very appreciative.