[UPDATE @ 6:24 PM PST] Rock on, I found out what it was: following a prompt reply from the fabulous Joe Cheng, I went to deactivate my WordPress plugins to narrow down what was causing the problem. Looks like Google Sitemaps (of which I'm using an older version, and oddly, unlike other plugins, it hasn't told me to upgrade) is the culprit, so I'm keeping it OFF for now. I may try upgrading it later if I have time. Time, ah time… where have you gone.
I just read the good word on Microsoft dev Joe Cheng's blog and am off to download the newest version of my favorite blogging software now.
Ever since upgrading to WordPress 2.3.1, I've encountered this annoying problem and hope I can find a resolution soon.