If an input field has a predefined value and you clear the field and send the form, WebKit will send the predefined value instead of an empty value. It works fine with last official Safari (417.9), but is buggy at least in WebKit 420+ (I am new to WebKit and use the Nightly WebKit builds provided by Mark Rowe) The above mentioned url is a simple test-page to demonstrate the issue.
This should be fixed in the next nightly. *** This bug has been marked as a duplicate of 6733 ***