Client side validation problem when using absolute positioning

[Toby Hobson]

I have just encountered a problem and wanted to run it by you guys before
reporting it as a bug:

have positioned an element using css absolute positioning but the validation
"bubble" appears in the wrong place. Here is my relevant code:

<t:div id="newSetPanel">
  <t:form>
    <t:errors />
    set name <t:textfield t:value="setName" />
    <input type="submit" />
  </t:form>
</div>

css:

#newSetPanel {
    width:300px;
    height:100px;
    border:solid 1px black;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-left:-150px;
    margin-top:-50px;
    background-color:white;
}

Page:

@Property
@Validate(value="required")
private String setName;

The bubble appears in the top left corner of the screen, not over the
textfield as I would expect

Toby