I did this myself just a few weeks ago. The complaints was that search results would often come back fast enough that the user may not understand anything was done if the results happen to be the same.
I wish I could find where I read this, but this used to be an issue with LED brake lights on cars, they would come on so fast that people had longer reaction times because they knew something had changed but couldn't put their finger on it instantly.
Saw a form recently with search-as-you-type that included a fake button that when pressed would write "Search Complete" to the screen, but had no other function, for users who didn't comprehend search as you type.
I got a bug-fix from the form developer that his button wasn't working, and I kept trying to explain to him that it couldn't possibly work, it didn't do anything.
Finally he explained that if the user had clicked the fake button already, and then changed their search to a search that reported the same results, it wasn't pretending to search again, and this was causing a lot of bug reports from his client.
I helped him rewrite the fake button to make a bigger deal about (fake) searching again, and apparently the bug reports went away.
