Removing edge weights from a Graph

This has to be a bug. I think Graph never really associates EdgeWeight with corresponding edges.

Here is a simplified example.

g = Graph[{1, 2, 3}, {
                Property[1 <-> 2, EdgeWeight -> x],
                         1 <-> 3,
                Property[2 <-> 3, EdgeWeight -> y]
                }];

gNew = RemoveProperty[{g, 1 <-> 2}, EdgeWeight];
gNew2 = SetProperty[{g, 1 <-> 2}, EdgeWeight -> Missing["Nonexistent"]];


Outer[
            PropertyValue[{#1, #2}, EdgeWeight] &,
            {g, gNew, gNew2},
            {1 <-> 2, 1 <-> 3, 2 <-> 3}
            ] // TableForm[#, 
                TableHeadings -> {{"g", "gNew", "gNew2"},
                 {1 <-> 2, 1 <-> 3, 2 <-> 3}}] & // Quiet

Notice the gNew row, how EdgeWeights are mis-aligned when the preceding one (i.e. x) deleted. And the 3rd column gives us a clue how PropertyValue extracts EdgeWeight -- that is, by Part.

I would definitely call this a bug.

---

The workaround I can come up with are two ways. The easy way is as I did for gNew2 -- instead of removing it, replacing it with a placeholder. While the hard way is to permute the to-be-delete edge to the end of edge-list before performing the delete:

myRemoveEdgeWeight[g_, e_] :=
    Module[{vl = VertexList[g], el = EdgeList[g], pos, ewl, ew},
        pos = Position[el, e];
        el = Insert[Delete[el, pos], e, -1];
        ewl = PropertyValue[g, EdgeWeight];
        ew = Extract[ewl, pos][[1]];
        ewl = Insert[Delete[ewl, pos], ew, -1];
        Graph[vl, el, EdgeWeight -> ewl] //
            RemoveProperty[{#, e}, EdgeWeight] &
        ]

PropertyValue[{myRemoveEdgeWeight[g, 1 <-> 2], #}, EdgeWeight] & /@
 {1 <-> 2, 1 <-> 3, 2 <-> 3}

{{1, y}[[3]], 1, y}

I should post this as a comment, but it is too long. Perhaps I'll delete it later.

There is also some nuisance with RandomGraph[]. Compare the following equivalent graphs:

n = 6;
g = CompleteGraph[n, EdgeWeight -> Range[n (n - 1)/2]]
WeightedAdjacencyMatrix[g] // MatrixForm
g1 = RandomGraph[{n, n (n - 1) /2}, EdgeWeight -> Range[n (n - 1)/2]]
WeightedAdjacencyMatrix[g1] // MatrixForm

Edit

Answering Szabolcs's comment:

n = 6;
g = CompleteGraph[n, EdgeWeight -> Range[n (n - 1)/2]];
w = WeightedAdjacencyMatrix[g] // MatrixForm;
g1 = RandomGraph[{n, n (n - 1) /2}, EdgeWeight -> Range[n (n - 1)/2]];
w1 = WeightedAdjacencyMatrix[g1] // MatrixForm;
Row[{w, w1}]