Was it an actual detection or just an Auto Sandbox trigger?
Autosandbox is set to "Ask", so it's hard to tell for me. This happens quite often with brand-new versions of both Base and Math - basically, the file prevalence is low.
Anyway, as in the past, the issue was solved quite soon.
By the way, on the new Avast! website I cannot find the link for reporting false positive...
EDIT: info added