Help with Vertical Slabs

Hi,
I'm trying to create vertical slabs for a modpack, as some blocks are missing it and others have it.
However, I'm having an issue where when I right click with a V Slab on an already placed V Slab I get the issue shown in this gif:
https://s6.gifyu.com/images/CopperVSlabIssue.gif

Where a slab is momentarily placed, and then vanishes before my double slab block appears.
Is there a way I can fix this?

My Procedures I use are here: