1.For the staircase the scissors phenomenon joints is that the top R/f in the landing slab is transferred as a bottom R/F in the waist slab and the bottom R/F in the landing slab is transferred as a top R/F in the waist slab.

2.The reasons behind this phenomenon is to prevent the crushing of the cover due to the resultant force. As resultant force will crush the cover as it is shown in the attached sketch