Ladders, vines, and scaffolding affect your movement even when standing on a solid block. When standing inside one while on the ground, your movement will be slowed and the controls will be more slippery as if you are climbing them. This also happens when sneaking on the side of a block while inside a climbable block.

This bug makes navigating through a jungle more frustrating, and can be somewhat annoying around ladders and scaffolding.