"I noticed that if you create a vApp and if you choose the option "Power on vApp after this wizard is finished", the 'Start vApp' blocking task is never kicked off."
I am going to go test this myself - this sounds bad. If you are seeing this please report it as a defect as a powering on Vapp should always have to send the blocking task off. (Otherwise IPAM and other integrations would not work correctly)