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:

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.