It seems that Google is trying to add (part of) the answer someone is looking for in the page's title.
I'm assuming from the original post that this might simply be a more extended version of title (and description) changes that Google has been making for years. The query has been a key factor in all of the changes I've seen.
Chances are that a mismatch between the query and the page title element might trigger the change, and that the added vocabulary is then pulled either from your site or from a site linking to your site. It would be interesting to know if this is still the case, and how far afield Google is now going to find appropriate text.
Originally, when Google changed titles and descriptions, it substituted ODP (Open Directory, dmoz.org) titles where available, if the ODP title was more descriptive of the query than your title was. Google also sometimes pulls a title from inbound link anchor text, where that anchor text better describes the query. If your meta description doesn't match the query, descriptions are pulled from text on your site. But in the past, there's generally always been some onpage source, on your site or on a linking site.
If you don't like the ODP text, Google does obey the robots element content attribute value... content="noodp"
, as in
<meta name="robots" content="NOODP">
Google describes its treatment of titles and descriptions here... Changing your site's title and description in search results
This is how Google suggests that you might track down the source of Google changes...
If you're concerned about content in your title or snippet, you may want to double-check that this content doesn't appear on your site. If it does, changing it may affect your Google snippet after we next crawl your site. If it doesn't, try searching Google.com for the title or snippet enclosed in quotation marks. This will display pages on the web that refer to your site using this text. If you contact these webmasters to request that they change their information about your site, any changes to their sites will be recognized by our crawler after we next crawl their pages.
Questions I'd asked now whose answers might be helpful...
- How extensive are the title changes?
- What kind of queries are they for?
- Where is the new text coming from?
- If from offpage, are they from your backlink pages only?