CKEditor does not always load in IE8

The CKEditor doesn't always load correct.
The first time it is loaded as expected, but second time it keeps showing a spinning wheel.

Also, a javascript error is generated:
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Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)
Timestamp: Thu, 5 Feb 2015 10:45:16 UTC

Message: 'b[...]' is null or not an object
Line: 206
Char: 304
Code: 0
URI: http://10.0.0.76:8080/cms/ckeditor/optimized/ckeditor.js?antiCache=1423131578191
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When setting the cacheTimeout of the CKEditorResourceServlet to 1 (instead of the recommended 86400 ms the editor is loaded as expected.