Merge pull request #441 from jorge-graca-sky/patch-2

fix: order same zIndex elements by updateTreeOrder

src/tree/core/ElementCore.mjs

@@ -2031,6 +2031,9 @@ export default class ElementCore {
                     a.splice(ptr);
                 }
             } else {
+                a.splice(n); // Remove items that were sorted in b array, so that we can sort a
++               // Beware that the function passed here to Array.sort must be stable
++               a.sort(ElementCore.sortZIndexedChildren); // Needed because items with same _zIndex may not be ordered by _updateTreeOrder
                 // Merge-sort arrays;
                 ptr = 0;
                 let i = 0;