After boot. I reckon it is when the Avast services load fully. Yes, latest version.
Already tried that. That’s where I’ve been enabling the shields I hadn’t installed when I was narrowing down which shields were causing locking.
I can now confirm it is not present in Windows Vista 32-bit SP2. My logic now says that the commonality between the two cases I have seen is possibly IE10, but I know it is working on my sister’s Windows 7 32-bit SP1 with IE10. Her case differs in that IE10 was installed AFTER Avast!, both problem cases had IE10 installed first and both were previously running Microsoft Security Essentials.