Ah, I didn't notice that it should be a feature not a bug. :-)
Have you tried Firebug?
Using Firebug you should try to find the location of an element in
your DOM whose id is "citybox". It's in the middle of the form and
includes the problematic dropdown box. This element - just as the
following element whose id is called "results" - are code relicts of
one my examples, namely this one
http://www.wolfpil.de/v3/map-in-a-box.html
It seems that you have copied and pasted the code in chaotic manner.
This wouldn't care anyone if the functions and listeners, that are
also still in your code, wouldn't be called.
Have a look at this listeners
<div id="results" .... onmousedown="dragstart(event)">
And the next td element
<td style="height:31px;background-color:#F5FFFA ...
onmousedown="dragstart(event)">
So at this point you should ask yourself if you still can find the
function dragstart() in your code and what it's doing. I'll try to
explain shortly and approximative: As soon as the function dragstart()
is called the global variable draggable is set to true. And because
there is also still a global event listener active that calls the
function watchMouse() this function is trying to set the position of
the elements mentioned above to the position of mouse cursor.
If you finally and definitely get rid of these wildly pasted fragments
one of the main problems of your map should be solved.