The provided description suggests that the IE browser does not load new CSS images after a stylesheet is changed. I am not sure why this happens, but you can compare your implementation with the following example, which works correctly in IE as well. You can also test the behavior on our online demo site (first remove the modal overlay of the Scheduler's edit form via the browser's DOM inspector).
Keep in mind that the discussed problem falls outside the scope of our technical support, because switching stylesheets on the fly represents a general web development task, which is not related to Kendo UI, does not require Kendo UI APIs to work, and depends on the browser behavior.
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