I created a custom theme for our web application with your kendo UI theme builder (http://demos.telerik.com/kendo-ui/themebuilder/).
Every component that we use so far were perfectly rendered with our custom style. This morning I started to use the ListBox but this component is not rendered correctly. After some research I found that style related to the list box are not included in the kendo.custom.css generated by the theme builder.
When I check the styles from your demo page (http://demos.telerik.com/kendo-ui/listbox/index), the styles related to k-listbox are present.