Hi,
I can just add that I to have seen the same kind of problem using hostscan 4.1.06020.
The policy editor just lets you choose the OS as "Windows 8" but the hostscan engine detects the OS as "Windows 8.1". This obviously does not match. Previously the engine detected it as "Windows 8". Yes that was wrong before but at least is matched what you could select in the policy, ie it was working. I suspect Cisco will soon realise this and fix it.
Meanwhile there is a simple "hack" you can do. The DAP-policy is stored in an xml-file on the VPN-headend. This file is called dap.xml.
Simply download that file, edit the xml so the OS version string says "Windows 8.1" instead of "Windows 8", that is in the snippets <name>endpoint.os.version</name> <value>Windows 8</value>.
Upload the file to the VPN-server again.
The VPN-server will handel this just fine, the only problem is when trying to edit such an entry in the ASDM GUI, it will not know what to do with it.
Best regards