Butter and shortening cannot be exchanged equally in recipes that are sensitive to the amount of water in them. Pie crust is one. Good shortening (Crisco) has no water. 12 grams of Crisco has 12 grams of fat. U.S. common butter typically has about 81 percent fat. European butter has more like 85%. And butter contains water. By directly substituting, you got less fat and added water, and I suspect the water did most of the damage. When water is a critical factor, and I want to use butter, I melt it and simmer away much of the water.
If you happened to follow the recent posted link to the America's Test Kitchen ginger snap recipe, you will have seen that the butter is simmered until it starts to brown. It removes much of the water to make the snaps drier and gives the snaps the browned butter flavor.
There are butter-only pie crusts, but dealing with the added water can be tricky, and it's easily removed.
"Kitchen duty is awarded only to those of manifest excellence..." - The Master, Dogen