Web Filtering Not Working in Chrome Unless Using Internet Explorer Initially

Question

We've got an issue on our UTM 9.602-3, whereby we have we filtering rules that do not get applied in Chrome, unless we access the require site in IE first. For example, we have Youtube.com blocked in our base policy but then we have a "Staff" policy that allows it if in the staff AD group. When accessing Youtube using Chrome, it gets blocked by the base policy, which is not how it should be. If we then access Youtube in Internet Explorer, it correctly allows it, as per the Staff policy. If we then go back into Chrome, Youtube is then allowed. Interestingly, when we initiall try and access in Chrome, there doesn't seem to be any valid entries in the web filtering log but then once we access in IE, the log is then populated. 
 I've blocked the quick protocol in our firewall, so I don't think it's to do with that. 
 Can anyone offer any advice? 
 Thanks

colly72 · Answer

After investigation, I believe that this issue is due to the limitations of transparent mode with AD SSO. The red herring with Internet Explorer I think is that its home page is a non https page, which I think will result in authentication taking place, whereas the Chrome startup page is https, resulting in authentication not occurring and thus the UTM falls back to the base web filtering policy. 
 Am i correct in thinking that once Internet Explorer authenticates, that Chrome will use this? That's the only explanation that I can conclude from what I'm seeing. 
 The workaround I'm using is to set Chrome to open up a non-https site when it starts up - this seems to have the desired effect and the policies then seem to work as they should. 
 The other option might be STAS - would this generally be a better option for domain machines when using AD SSO in transparent mode?