It's an AV vendor issue. For whatever reason some AV vendors flag MC33's files (specifically in this case the MC33 installer), even though they've been digitally signed with an extended validation certificate (which are expensive to get and *should* be given more consideration when flagging as a false positive as no malware is going to go through all the trouble to get a EV cert and sign malware with it, but AV vendors like Avast/AVG don't do that).
In a perfect world any AV detecting potential malware on a file signed with an EV cert should have the sense to at least automatically submit a sample of the file(s) to the AV vendor for deeper analysis as the chances of a false positive on an app signed with an EV cert would be higher compared to a "normal" app.
Avast/AVG are the main two right now with this false positive detection according to VirusTotal. Avast and AVG are owned/developed by the same company, so it doesn't surprise me in the least. Personally I'm not fond of either one (and both are pretty low on my AV vendors people should consider list), both has had serious issues in the past and I wouldn't let either one of them protect a toaster much less a PC, but that's my point of view.