This seems to be based on some old version. Look at the number of extensions that come from PenguinMod and TurboWarp. Anyway, look at what happens when you drag out a block with a circular dropdown (as in the dropdowns that allow reporter blocks to be inserted) or move those blocks around
Edit: I can add extensions and the blocks keep stacking on top of each other, though I can't add extensions that come from SharkPool's extension gallery. The addons appear to be the same version
