Fatal Error – Weak Escape?

Since updating to 2.8.1 (and now 2.8.2), I’ve been getting this error message when trying to add or edit a post:

Fatal error: Call to undefined function: _weak_escape() in /home/bdunc1/marketinginprogress.com/wp-includes/wp-db.php on line 487

I can still publish the post, eventually, but it creates multiple drafts about every 20-30 seconds, and it always goes to a screen with only this message once I push save or publish. I’ve manually installed the wp-includes file as has been recommended, but that didn’t help. Any other suggestions on how to fix this?

bd