Google has stated that they reserve the right to change the page/meta title if they believe a different title is more useful to users. This could be what is happening, particularly if the text they are showing is contained somewhere else within the content on the page.
Cutts says Google wants to show the titles that it thinks are most useful. "For example, suppose the title of your page is ‘Untitled’ or if there is no title. If that’s the case, we try to show a relevant, useful title."
"We reserve the right to try to figure out what’s a better title, what’s a more descriptive title or snippet to show the users,"