jQuery UI Dialog - missing close icon

I'm using a custom jQuery 1.10.3 theme. I downloaded every straight from the theme roller and I have intentionally not changed anything.

I created a dialog box and I get an empty gray square where the close icon should be:

I compared the code that is generated on my page:

<div class="ui-dialog-titlebar ui-widget-header ui-corner-all ui-helper-clearfix">
    <spanid="ui-id-2" class="ui-dialog-title">Title</span>
    <button class="ui-dialog-titlebar-close"></button>
</div>

To the code generated on the Dialog Demo page:

<div class="ui-dialog-titlebar ui-widget-header ui-corner-all ui-helper-clearfix">
    <span id="ui-id-1" class="ui-dialog-title">Basic dialog</span>
    <button class="ui-button ui-widget ui-state-default ui-corner-all ui-button-icon-only ui-dialog-titlebar-close" role="button" aria-disabled="false" title="close">
        <span class="ui-button-icon-primary ui-icon ui-icon-closethick"></span>
        <span class="ui-button-text">close</span>
    </button>
</div>

EDIT

The different parts of the code are generated by jQueryUI, not me so I can't just add the span tags without editing the jqueryui js file which seems like a bad/unnecessary choice to achieve normal functionality.

Here is the JavaScript used that generates that part of the code:

this.element.dialog({
    appendTo: "#summary_container",
    title: this.title(),
    closeText: "Close",
    width: this.width,
    position: {
        my: "center top",
        at: ("center top+"+(window.innerHeight*.1)),
        collision: "none"
    },
    modal: false,
    resizable: false,
    draggable: false,
    show: "fold",
    hide: "fold",
    close: function(){
        if(KOVM.areaSummary.isVisible()){
            KOVM.areaSummary.isVisible(false);
        }
    }
});

I'm at a loss and need help.

I am late to this one by a while, but I'm going to blow your mind, ready?

The reason this is happening, is because you are calling bootstrap in, after you are calling jquery-ui in.

Literally, swap the two so that instead of:

<script src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script>
<script src="js/bootstrap.min.js"></script>

it becomes

<script src="js/bootstrap.min.js"></script>
<script src="http://code.jquery.com/ui/1.10.3/jquery-ui.js"></script>

:)

Edit - 26/06/2015 - this keeps attracting interest months later so I thought it was worth an edit. I actually really like the noConflict solution offered in the comment underneath this answer and clarified by user Pretty Cool as a separate answer. As some have reported issues with the bootstrap tooltip when the scripts are swapped. I didn't experience that issue however because I downloaded jquery UI without the tooltip as I didn't need it because bootstrap. So this issue never came up for me.

Edit - 22/07/2015 - Don't confuse jquery-ui with jquery! While Bootstrap's JavaScript requires jQuery to be loaded before, it doesn't rely on jQuery-UI. So jquery-ui.js can be loaded after bootstrap.min.js, while jquery.js always needs to be loaded before Bootstrap.