The bug is this: with scaffolding, if you spam, you can create a scaffold block that floats in the air (without support). If you click on this block, this creates a new scaffold block but removes the old one. A shift + click removes this buggy block.
It's like a ghost block but you can see it and use it like a normal block
With this bug, you can use the scaffold for travel (using jump and placing at same time)