Unable to add stairs to Wedges

Game mode: [Online | Custom]
Problem: Bug
Region: [Here]

Many of us building a building will use wedges to create an arrow station on a side of a building and with 3 or 6 wedges you can create a nice triangular design however for other reasons sometimes you want to add stairs to the wedges and I found this to be impossible even with support laid down.

Steps on how to reproduce issue:
1.create a wall using foundations in a single line 5 long and 5 high
2. Choose a side and between the 2nd and 3rd foundation attach 3 to 6 wedges to make the platform
3. try to then attach stairs to the wedges to be able to walk up the stairs to stand on the wedge platform.