Administrators may add in the Virtual Proxy "Additional response header" setting "Pragma: no-cache" in order to prevent caching of pages. After this the Qlik Sense Hub/QMC special Fonts and Symbols (used as Icons) will display unknown symbols when opened in Microsoft Internet Explorer.
Microsoft IE bug: https://connect.microsoft.com/IE/feedbackdetail/view/992569/font-face-not-working-with-internet-explorer-and-http-header-pragma-no-cache
Remove Pragma: no-cache" from Virtual Proxy's configuration; Sense includes Response Header "Cache-Control: public, must-revalidate, max-age=0", which should have similar effect of "Pragma: no-cache" or "Cache-Control: no-cache" when using HTTP/1.1. However, clients relying on HTTP/1.0 header (HTTP/1.1 disabled) do not have the new 1.1 specifications and may cache pages if Pragma is not included.