Yeah, for the first pick you can't place on that spot so that the 2 would be pointing up or down. It is indeed intentional design limitation mainly because I wanted the bone rotation to be automatic based on the placement and if that one spot allowed three different rotations, it would require user to rotate manually. And btw, even if you had placed it pointing down on that spot, connecting that to the other 2 wouldn't be allowed either as it would make the bone sides touch.
Kinda same with that other picture and the double 4. Could place it there if the other side had a bridge to link to though. Understandable that these limitations can be frustrating especially since I guess they aren't obvious to anyone else besides me. But on the other hand, limitations also bring up the need for better placement planning and hence raises the skill ceiling.
And the tutorial dude dodges mouse cursor so you can always shoo them away if it's covering something...