A WebmasterWorld thread has discussion over how Google handles the mass changing of title tags.
In this particular case, a webmaster copied the structure, not the design, of a site to a new site. When they copied it over, they forgot to change the title tags, although the content, design and images are all unique from the previous site. Soon after, they changed the title tags to make them all unique to the content on those pages. Four months later, the title tags Google shows in the search results are the same as they were - i.e. the old, wrong title tags.
Since this is a WebmasterWorld thread, we do not know the specific site having trouble. So as you can imagine, it is incredibly hard to diagnose the issue.
jdMorgan, WebmasterWorld administrator, said:
The one thing that Google "hates" is large, sudden changes. So I'm going to recommend that you grit your teeth and wait it out instead of giving G yet another reason to think your pages are 'suspicious.' Build links, expand and update content -- anything productive to keep your mind off this embarrassing mistake, and suggest that an official "acceptance testing" program (with a formal list of things to check off, including <title> and <meta name="description"> tags) be put into place for new developments so that this won't happen again.
Keep an eye on Googlebot, and once the pages in question have been spidered a couple of times, this situation should resolve itself. It's very hard to be patient and "do nothing," but that's what it takes in this situation; Working on the other aspects of improving the site will help -- both practically and emotionally...
Of course, if he wanted specific advice about his web site, he should go to Google Webmaster Help. However, many people avoid that inorder to keep their anonymity.
Forum discussion at WebmasterWorld.