WebDav: request filtering not working

I've set up a website in IIS on Windows Server 2008 R2. I've configured WebDav and I'm able to connect. 

We've some iPads with the GoodReader app, which connects by WebDav and its working as expected.

So far so good.

GoodReader has some limitations with various file types. For example, if there is a MSG file, GoodReader fails to sync.

I want to use Request Filtering to hide the files who give problems. To test the Request Filtering function, I added the following lines to applicationhost.config:

<requestFiltering><hiddenSegments applyToWebDAV="true"><add segment="test.txt" /></hiddenSegments><fileExtensions applyToWebDAV="true"><add fileExtension=".txt" allowed="false" /></fileExtensions></requestFiltering>

I've a file named 'text.txt', but this file is still visible when I connect by WebDav.

In the IIS Manager, the lines are visible in the Request Filtering, so the config-file seems applied.

Could anybody help me out of this? Your help is really appreciated.