AutoCompleteTextField - gives a type mismatch error on IE - version wicket-1.4-rc1

wicket-autocomplete.js
function function showAutoComplete()
line 291 container.style.zIndex=(!isNaN(Number(index))?Number(index)+1:index);

looks like IE doesn't like big i in zIndex, IE seem to be be happy with zindex

not sure if that's the correct way to resolve the issue.