OK, this issue exists. And I don't think that it is hard to produce. Because both my son and myself have produced it on 2 different computers.
This was after watching the videos. This is using the demo version. This is using standard pieces.
Yes we can load the tutorial and yes it works. We can even hack up the tutorial and it still works.
But the only way I can get past the top of the stairs on anything created from scratch, is to remove the second level and let the character walk past the top pf the stairs. So somehow the floor of the second level is somehow blocking it.
Since the loading the tutorial and running it works and making one doesn't, it occurred to me that saving my level and running elsewhere would have the bug. Attached is a level I created with the issue.
I was near purchasing the product for my son, but this is a show-stopper.
Chris Lopeman