Okay, I encountered that "ghost block" again (not sure what else to call it, lol).
I had clicked off the grid button. When I moved it back over the Grid button, it said "toggle grid" as normal. When I moved the mouse over the Extension button, that small box appeared for a bit. This only happened when toggle grid was displayed above the button.
It's a tooltip issue
Okay, I encountered that "ghost block" again (not sure what else to call it, lol). I had clicked off the grid button. When I moved it back over the Grid button, it said "toggle grid" as normal. When I moved the mouse over the Extension button, that small box appeared for a bit. This only happened when toggle grid was displayed above the button.