I'm currently experiencing this exact same issue. Did you ever discover a fix or workaround for this? Or are you still running AV 2.12.0?
We're on 2.14 and have the same issue.
Isn't this related to that darn February patch as well?? As it seems to try and find a file it cannot see and redirects to the mountpoint folder.
Users were also unable to install MSI's in our environment with that patch installed, so it was not just related to the packaging machine.