Glad you've figured it out but boy that doesn't make sense. The powerhead can spin either way, so if the prop was upside down it just needs to spin the other direction if it's going backwards at startup.
Oh well, apparently I'll just hurt myself if I think about it any longer ... so I'm not going to.
Either way I'm glad you figured it out. But yeah, these kits are good for giving you flow in a hurry without spending gobs of cash, but that's about it. Like anything I guess ya gets what you pays for.