Thanks for all the great screenshots of the stairs problem. I made some changes, and it is now possible to do that:
The problem was that the stairs connected unnecessarily to a neighbor block of stairs, forming a corner, when the neighbor was a corner itself. This is now fixed. The whole system is a bit complicated, but nowhere near as complicated as wires/electricity implementation ;-)
Stairs/slabs lighting is still a little bonkers, but this is a job for another update.
I will be releasing full version of 1.29 on Google Play soon.