I noticed this as well for some pages on one of my sites. After comparing results with a webmaster on another forum, I've come to the conclusion that Yahoo is incorrectly using 'old' <title> tag text. For example, one of my pages is displaying <title> tag text that I was using last summer and through most of autumn. I changed this <title> tag text 2 months ago. Yahoo picked up on the new <title> tag text about a week after I changed it and then displayed in properly in the SERPS right up until about a week ago. Then it suddenly started glitching out and displaying my old <title> tag text (except with all the words that weren't proper nouns displayed in lower case).