Yeah but then other issues will pop up, I see what you are saying though.
Maybe if they just concatenate them instead of stacking (just along the first dimension) this problem does not show up.
Also, to me the most important dimension is the first one (as it said in the error  Sizes of tensors must match except in dimension 0), it makes sense to have the dimension 0 to be the same, but i can digest to have all dimensions the same