Have you tried using more normal mouse double-click settings?
The double-click distance as well as the time may be a factor, if that has also been changed in the registry.
I don't remember any similar reports about that, and this should really be in a separate thread.
Does it only happen with exe files / installers? If so, it's probably antivirus going wrong when it scans them.
Could also be a Copy Hook something has installed (Preferences / Miscellaneous / Shell Extensions can show you them).
Or it might happen if you've customised the drag & drop actions (Settings > File Types) with something unsuitable for them.