UCAIR toolbar changes the semantics of Back button of the web browser. Using Internet Explorer with UCAIR toolbar, when the user clicks one result of search result page and then clicks the Back button, the user will see different contents of search result page. This is because the UCAIR personalized search agent updates the user model immediately after the user makes an action (click a result link) and rerank the search results according to the updated user model. So the user will see reranked search result page, which probably is different from the page previously seen by the user. Thus the semantics of back button has changed after the installation of UCAIR toolbar.
During several demos of UCAIR toolbar, many people are interested in the semantics change of the back button. A lady said she would like to see the same stuff as before after clicking the back button. Some people are interested in how to minimize the confusion brought to the user with the semantics change such as where pushed up results should be places if UCAIR toolbar has to change the semantics of the Back button.
I found the breaking of Back button was considered to be one of top web design mistakes by Jakob Nielsen in 1999. The semantics of Back button is a question for the web design now, especially with many dynamic web design techniques such as Ajax. What does the user expect when he clicks the Back button? Probably the answer will not be consistent. There is some research works on the Back button of web browser such as Getting Back to Back by Saul Greenberg and Andy Cockburn.
