If they don't realise that the detection is from the anti-rootkit scan the normal signatures have no effect, as you found in the VT results.
So when the alert comes up, I take it that is the Suspicious Files found rather than Rootkit found, etc. ?
If so You have two options and the default Ignore is the one you should select, don't check the 'Don't tell me about these files in the future (as you would never know if this is resolved and I don't know if you can reverse this decision). Whilst this will mean it will come up in future boots, telling avast to Ignore should trigger the CommunityIQ to report this back to avast and should get analysed and hopefully corrected soon.
That doesn't stop you sending the sample file to avast with as much information as possible about the alert being the anti-rootkit scan 8 minutes after boot, your OS, Graphics card and the driver version, etc. A link to this topic wouldn't hurt.