In release notes for update 9, it says windows 8.1 support was begun with update 8.
I submitted the full sources for my case in IPS 6000037395 which reports "waiting for customer" since over 3 weeks ago after I verified that the case works without internal error on win7 on an original core-i7 (running Intel64 mode in both cases). The initial response, asking for the win7 comparison and sources, was prompt.
Was Windows 8.1 support withdrawn in update 9?
Support for 8.1 is still present in Update 9.
I checked the logs on that IPS issue, it clearly shows that the last communication was from you on the 26th, but says "waiting for customer". I am guessing that there was a glitch in the system. I will change the status and ping Kirill directly to get back to you with where he is on the issue.
In case I've escaped moderation, I'll thank Holly again for apparently unblocking 2 issues on the IPS gateway site
1) Kirill not being notified when I added comments and source files
2) the email notices coming to me with broken URL references