The bug
Corner stairs with torch/lever/button etc. doesn't cause block update when near destroyed support stair
To reproduce
Place corner stairs (as in the screenshot)
At the corner steps, place the block that needs the support (lever, torch, etc.)
Break the non-cornered stairs
The lever / torch / button does not drop out when those stairs were broken.
That's caused by the fact that the server doesn't save that block state, and as such, the block does not seem to update in the server's perspective.
This is fixed once MC-105922 is fixed.