Slabbed

Fixed: scaffolding placed on a slab (a lowered scaffolding column) is now stood on at its real height. Scaffolding has no solid body - its only collision is a thin standing layer that Minecraft switches on when your feet are above the top of the block. That check was still comparing against the unlowered block, so on a lowered column you climbed to the top, then sank and slid back down as soon as you released jump. The check now uses the lowered height, so you stand where the scaffolding is drawn. Scaffolding on plain ground is unchanged.

Version note: this hotfix is numbered alpha.10 because alpha.8 and alpha.9 belong to the Fabric 1.21.1 line (Slabbed's alpha numbers are one shared series across all versions).