" 'broad match' bidding advertisers are doing is now getting more and more broad in terms of keyword matching and maybe even session timeThis has been confirmed by Google in this AdWords Help page. Here is the relevant text.
In other words Google is entering behaviour targeting and search profiling. For logged in users it is clear that no set of search results will be the same.
II. How does this feature work?
This feature is an enhancement of broad match. It works by generating similar terms for each search query based on the content of the current query and, if deemed relevant, the previous queries in a user's search session. Your ad will potentially show if one of your broad-matched keywords matches any of these similar terms.
Thanks to "Kate" for sending through the link.