Many searchers were complaining in a Google Web Search Help thread yesterday that their search queries were disappearing. Google later confirmed the bug. What was/is happening for some searchers is that they enter their search query into the Google search box, hit enter and on the next screen the search query is no longer shown in the search box.
There are a few threads out there on this, but only one with confirmation from Google. The first report said:
When I press enter OR the search button, the text within the searchbox simply disappears rather then directing me to a search. This only happens after my first search, i.e. any subsequent searches after searching for something from the Google's main page.
Jaime from Google eventually replied saying they think they fixed the issue:
We've just finished pushing a fix for this bug. If you're still having problems with your search query disappearing from the search box, please let me know.
It does seem to now be resolved for everyone, and I don't believe anyone captured video screen cast of how this bug worked exactly.
Forum discussion at Google Web Search Help.