Thanks, WPyogi, that fixed it.
The site you pointed me to found an error in a very specific location in some post. I went to that post, and everything looked fine, but at that very spot in the text, something was odd. I had to click an arrow key twice to pass a seemingly empty spot in the text. There must have been some strange invisible object or something hiding out there. That was the only hint of a problem I got in either the visual or text mode. Well, I deleted the mystery 'nonexistent' object with backspace, and it all works now.
Strange, I wonder what exactly the issue was. Thanks again for your help!
