Sorting breaks re-squarifying.

[mbostock]

The squarified treemap layout hides metadata in node._squarify so that it can perform a stable update of a squarified layout. However, if node.sort is called in the interim, then the order of nodes change, breaking the meaning if node._squarify (which is currently one plus the index of the last node in the current row).

The desired behavior is that the squarified layout is remains stable even after sorting, effectively ignoring the sort. (The nodes would be reordered, but retain their relative positions.)

One way to fix this would be to store the rows as arrays of nodes rather than indexes, such that any reordering of the children does not affect the stored metadata.