fixed mobx strict run-time exception when opening the presentation trail, then dragging a collection menu item into it.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/client/views/collections/CollectionStackingView.tsx b/src/client/views/collections/CollectionStackingView.tsx
index 5c28d8969..41e2ad81a 100644
--- a/src/client/views/collections/CollectionStackingView.tsx
+++ b/src/client/views/collections/CollectionStackingView.tsx
@@ -292,7 +292,7 @@ export class CollectionStackingView extends CollectionSubView<StackingDocument,
             });
             const oldDocs = this.childDocs.length;
             if (super.onInternalDrop(e, de)) {
-                const droppedDocs = this.childDocs.slice().filter((d: Doc, ind: number) => ind >= oldDocs); // dropping a document that wasn't in the list or one that creates something new (eg., a button that creates a note) adds a document to the end of the list
+                const droppedDocs = this.childDocs.slice().filter((d: Doc, ind: number) => ind >= oldDocs); // if the drop operation adds something to the end of the list, then use that as the new document (may be different than what was dropped e.g., in the case of a button which is dropped but which creates say, a note).
                 const newDocs = droppedDocs.length ? droppedDocs : de.complete.docDragData.droppedDocuments; // if nothing was added to the end of the list, then presumably the dropped documents were already in the list, but possibly got reordered so we use them.
 
                 const docs = this.childDocList;