Simplifying not working as expected for 1 branch

So I thought I had a pretty good grasp on tree structures, but have either encountered a bug or a don't understand something.

So if I merge several trees, each simplified and with a depth of one, everything works as expected.

Spread A:

{0} 10 items

{1} 5 items

{2} empty

Spread B:

{0} 3 items

{1} empty

{2} 4 items

Merged:

{0} 13 items

{1} 5 items

{2} 4 items

Fine.

But now I have the situation that the number of branches can go down to 1, resulting in simplify effectively flattening the list, but merge somehow "remembers" the data structure and will result in something like:

Merged:

{0} 1 items

{0;0;0;0;0;0} 100 items

So this is happening even though all inputs are simplified. Shouldn't simplify also reduce all the items to just {0}, even when just one branch is present?

So is this expected behaviour? Surely the number of branches should be irrelevent for simplify.

Any workaround? I tried trim tree, but it fails because there is one branch with the correct {0} identifier. Basically it should flatten in that case, but not when there is more than 1 branch.

In the screenshot, D2 contains no data, but D1 is simplified, but retains its depth information and should also be {0}, as it does for any data that has more than 1 branch. The merge component makes it visible. Flattening is not an option.