This article describes what to do to fix IE11 when you use the RadCompression and .browser file implementation of Hidden field viewstate compression. When we were fixing this issue we found that the solution doesn't work for certain builds/versions of IE11, specifically the version shipped on touch devices. The userAgent string has additional attributes that interrupt the string from matching the RegEx in the IE11 browser node. We modified the expression to the following and it successfully corrected our issue on touch and non-touch versions of IE:
<browser id="IE11" parentID="Mozilla">
<userAgent match="Trident\/7.0;(?:(?: Touch;)?(?: \w*;)?)? rv:(?:(?'major'\d+)(\.(?'minor'\d+)?)(?'letters'\w*))(?'extra'[^)]*)" />
<userAgent nonMatch="IEMobile" />
Hope this helps anyone that may run into that scenario.