High Posting Rate
If you make a large number of posts in a single day, you will be required to complete a word verification for each one, independent of whether your blog has been cleared as a potential spam or not. If this happens to you, simply complete the word verification for each post, or wait 24 hours, at which point it will be removed automatically.
Another thing to blame the forest fires on. Too much time on my hands and now Blogger pulls this crap.