Butter and Malt biscuits

korbo, Aug 5, 9:59pm
Made a slice that you crush the malt biscuits, and add 200gm melted butter.Particularly used butter that contained no water.
The topping cooked, but base is all crumbly.
This happened once before and I blamed the butter.

Does anyone have any idea what causes this, is it the butter or something changed in the buscuits.!