To work around the issue, you can use the parameter complete=0
in the Google address to turn off Google's autocomplete.
In Opera, for example, you can make a bookmark to http://www.google.com/?complete=0
with nickname google. You can then go to the address box, type google, and press Enter to start a Google search session with autocomplete off.
Or you can go to Tools → Preferences → Search, edit the Google entry and add &complete=0
to the end of the address. Then the Google selection in Opera's search box will use Google with autocomplete off.
###Test steps###
Test steps
I'm using Windows XP and Opera 10.1. I went to Google → Search Settings and turned off Google Instant.
I went to http://www.google.com/search?q=THIS+IS+VERY+UNIQUE+SEARCH+QUERY. When I clicked in the search box on the page and typed a letter, I could see the progress bar quickly flash in the address box indicating something was loaded. It seems that if I'm still holding a keyboard key down when the progress bar disappears, then the text cursor moves to the end of the search box.
If I go to http://www.google.com/search?q=THIS+IS+VERY+UNIQUE+SEARCH+QUERY&complete=0 then the bug no longer happens.