Try to type a ( into the search field. Nothing will happen. If you type a letter first, the ( will act like the down arrow.
Confirmed with a local debug build of WebKit r26819 with Safari 3 Public Beta v. 3.0.3 (522.12.1) on Mac OS X 10.4.10 (8R218).
Happens with the earliest WebKit nightly, r11976, on Mac OS X. Happens with Safari for Windows 310a18 seed. Happens in Opera 9.22, but not in Firefox 2.0.0.7.
I cannot reproduce this with Safari 3.1.2 on Mac OS X 10.5.5.
It was not reproducible later in 2008 and this bug does not have any reduction or test case to reproduce this issue, I am going to assume, it was fixed along the way but mark this as "RESOLVED WONTFIX". If you have any test case to reproduce this from archive or any more details, please reopen this bug. Thanks!