If this is the same problem I just fixed then the question isn't referring to the IE10 "clear field" X. It's referring to a very large text "X" character that is displayed in the Select widget in addition to the options that are supposed to be there, making the widget twice as tall as it should be.
In my case it was because I was mixing the CSS stylesheet from one Dojo version with the API's from another. Check to make sure that your stylesheet and dojo.js versions match. For example, in my case the stylesheet was:
...href="//ajax.googleapis.com/ajax/libs/dojo/1.7.5/dijit/themes/claro/claro.css" media="screen">
while the script being included was
... src="//ajax.googleapis.com/ajax/libs/dojo/1.10.1/dojo/dojo.js"></script>
I blame the fact that I was modifying Dijit sample code without knowing what the heck I was doing...