Engine Version: 4.10 on branch master(08.19.2015)
Only occures when the editor starts the launcher itself!
I noticed that the Epic Games Launcher seems to ignore the -http=wininet command when it is started in the standard community tab. If it started in the marketplace tab, everythings working fine.
So OpenLauncher(false, TEXT("ue/marketplace"), TEXT(-http=wininet)); works fine whereas OpenLauncher(false, TEXT("ue"), TEXT(-http=wininet)); ignores the command.
I believe the OpenLauncher does not support command line arguments any more, but i have forwarded the issue to another developer to see if there is a work around you could use.