27 Nov 2008
16 Apr 2012
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If it doesn't work then it definitely is a bug, but before we assume that:
1 - Have you enabled the filter (that is the text field below) by setting it to "true"?
2 - Once you have specified a filter, have you restarted the application from the IIS?
3 - Before restarting the application from the IIS, have you deleted all the cookies and the browser history?
You can even re-save the Web.config which will also ensure that the WebApplication will refresh all its caches.
Do all that for each combination of file extensions, and if it does not work, then it has to be a bug.
I will say this about Sitefinity, those help prompts under the text fields are a bit useless if they don't have an example of the format that the text entered has to be like. Since you can have comma separated elephants, it would help to see the pattern.