Sencha Touch, an iframe is shown when selectfield is opened

Question

I've got a problem when changing the selectfield item in Sencha Touch 2.3.0. As shown in the picture below, I got a "blue screen" whenever I try to drag the selectfield item to change its value.

When I used the inspect-element on Chrome, I realized that it is an iframe.

So I tried to "remove" the iframe by setting it in the CSS

iframe {
    display: none !important;
}

on top of index.html but it didn't work. so I tried another method in CSS

iframe {
    visibility:hidden !important;
    width: 0px !important;
    height: 0px !important;
}

and it still didn't work, the blue screen is still there. How can I remove this iframe?